Lesson 43: Operations on XML Elements

Editing an XML Element

Introduction

In some cases, you may want to perform an operation on an existing and particular node. For example, you may want to change the value of a node, you may want to add a new child node to an existing node, etc. Before taking any of these actions, you must be able to locate or identify the desired element.

Locating an element consists of looking for a particular node among the nodes. To do this, you must start somewhere. Obviously, the first node you can identify is the root. Once you get the root, you can then get a collection of its children. After getting a collection of the children of the root, you can locate a node in the collection. If the node you are looking for is a child of that first collection, you can then get a collection of the child nodes of that node and proceed.

The System.Xml namespace provides various means of looking for a node in an XML file.

Locating an Element Using its Index

Consider the following XML file named videos.xml:

<?xml version="1.0" encoding="utf-8"?>
<videos>
  <video>
	<title>The Distinguished Gentleman</title>
	<director>Jonathan Lynn</director>
	<length>112 Minutes</length>
	<format>DVD</format>
	<rating>R</rating>
  </video>
  <video>
	<title>Her Alibi</title>
	<director>Bruce Beresford</director>
	<length>94 Minutes</length>
	<format>DVD</format>
	<rating>PG-13</rating>
  </video>
  <video>
	<title>The Day After Tomorrow</title>
	<director>Roland Emmerich</director>
	<length>124 Minutes</length>
	<format>DVD</format>
	<rating>PG-13</rating>
  </video>
  <video>
	<title>Other People&#039;s Money</title>
	<director>Alan Brunstein</director>
	<length>114 Minutes</length>
	<format>VHS</format>
	<rating>PG-13</rating>
  </video>
</videos>

We know that the XmlNodeList class is equipped with both a method and an indexed propery named Item. Their syntaxes are:

public abstract XmlNode Item(int index);
public virtual XmlNode this[int i] { get; }

These two members allow you to access an element based on its index. Here are examples:

using System;
using System.IO;
using System.Xml;
using System.Windows.Forms;

namespace VideosCollection
{
    public partial class Form1 : Form
    {
        public Form1() => InitializeComponent();

        private void btnVideosCollection_Click(object sender, EventArgs e)
        {
            string strVideosFile = @"C:\Videos Collection\Videos.xml";
            XmlDocument xdVideos = new XmlDocument();

            if (File.Exists(strVideosFile))
            {
                xdVideos.Load(strVideosFile);

                XmlElement xeRoot = xdVideos.DocumentElement;
                XmlNodeList xnlVideos = xeRoot.ChildNodes;

                MessageBox.Show(xnlVideos[1].InnerText, "Video Collecton");
                MessageBox.Show(xnlVideos.Item(3).InnerXml, "Video Collecton");
            }
        }
    }
}

This would produce:

Locating an Element Using its Index

You can use this characteristic to locate a node. Because XML is very flexible with the names (you can have two child nodes that have the same name) and values (you can have two child nodes that have the same value) of nodes, when creating an XML file, it is your responsibility to create a scheme that would eventually allow you to uniquely identify each element.

Locating an Element Using its Name

To assist you with locating the first child node of a node, the XmlNode class is equipped with an indexed property (named Item) overloaded with two versions. One of the versions is declared as follows:

public virtual XmlElement this[string name] { get; }

This indexed property takes the name of a node as argument. After the property has been called, the parser checks the child nodes of the element on which the property was applied. If the parser finds a node with that name, it returns it as an XmlElement object. Here is an example:

using System;
using System.IO;
using System.Xml;
using System.Windows.Forms;

namespace VideosCollection
{
    public partial class Form1 : Form
    {
        public Form1() => InitializeComponent();

        private void btnVideosCollection_Click(object sender, EventArgs e)
        {
            XmlDocument xdVideos = new XmlDocument();
            FileInfo fiVideos = new FileInfo(@"C:\Videos Collection\Videos.xml");

            if( fiVideos.Exists == true )
            {
                xdVideos.Load(fiVideos.FullName);

                XmlElement xeRoot     = xdVideos.DocumentElement;
                XmlNodeList xnlVideos = xeRoot.ChildNodes;

                MessageBox.Show(xnlVideos[1]["director"].InnerText, "Video Collection");
                MessageBox.Show(xnlVideos.Item(3)["format"].InnerXml, "Video Collection");
            }
        }
    }
}

Based on the videos.xml file we had earlier, this would produce:

Locating an Element Using its Name

If the node has more than one child with the same name, then it would return the first child with that name. You can use this characteristic to look for, or locate, an element.

Locating an Element Using a Tag Name

To assist you with finding a node, the XmlDocument class is equipped with a method name GetElementByTagName which is overloaded with two versions. One of the syntaxes used is:

public virtual XmlNodeList GetElementsByTagName(string name);

This method takes as argument a string. The string must be the name of a node. If at least one node that holds that name exists in the file, this method returns a collection of the nodes with that name. If there is no node with that name, the collection is returned empty and there is no exception thrown.

Here is an example of calling the method:

using System;
using System.IO;
using System.Xml;
using System.Windows.Forms;

namespace VideosCollection
{
    public partial class Form1 : Form
    {
        public Form1() => InitializeComponent();

        private void btnVideosCollection_Click(object sender, EventArgs e)
        {
            XmlDocument xdVideos = new XmlDocument();
            string strVideosFile = @"C:\Videos Collection\Videos.xml";

            if (File.Exists(strVideosFile))
            {
                xdVideos.Load(strVideosFile);

                // Get a reference to the root node
                XmlElement xeRoot = xdVideos.DocumentElement;

                // Create a list of nodes whose name is Title
                XmlNodeList xnlTitles = xdVideos.GetElementsByTagName("title");

                foreach (XmlNode node in xnlTitles)
                    MessageBox.Show(string.Format("Inner Text: {0}", node.InnerText), "Video Collection");
            }
        }
    }
}

This would produce:

Locating an Element Using a Tag Name

Once you have a list of the nodes of a particular criterion, you can then act as you see fit. For example, you can look for a particular node that holds text of your choice.

Updating an Element

Consider the following version of our Videos.xml file:

<?xml version="1.0" encoding="utf-8"?>
<videos>
  <video>
    <title>Her Alibi</title>
    <director>Bruce Beresford</director>
    <length>94 Minutes</length>
    <format>DVD</format>
    <rating>PG-13</rating>
  </video>
  <video>
    <title>The Day After Tomorrow</title>
    <director>Roland Emmerich</director>
    <length>124 Minutes</length>
    <format>DVD</format>
    <rating>PG-13</rating>
  </video>
</videos>

The .NET Framework implementation of XML provides various options to change the aspect, structure, or value(s), of an element. For example, you can use the same logic used in collection classes. This consists of locating a node and simply changing its value(s). Here is an example:

using System.Xml;

public class Exercise
{
    public static int Main(string[] args)
    {
        string strVideosFile = @"C:\Videos Collection\Videos.xml";
        XmlDocument xdVideos = new XmlDocument();

        // Open the XML file
        xdVideos.Load(strVideosFile);
        XmlNodeList xnlVideos = xdVideos.DocumentElement.GetElementsByTagName("title");

        foreach (XmlNode xnVideo in xnlVideos)
        {
            if (xnVideo.InnerText.Contains("The Day After Tomorrow"))
            {
                xnVideo.ParentNode.InnerXml = "<title>Day After Tomorrow (The)</title>" +
                                              "<director>Roland Emmerich</director>" +
                                              "<year>2004</year>" +
                                              "<length>124 Minutes</length>" +
                                              "<format>DVD</format>" +
                                              "<rating>PG-13</rating>";
                                              
                xdVideos.Save(strVideosFile);
                break;
            }
        }

        return 10_101;
    }
}

This would produce:

<?xml version="1.0" encoding="utf-8"?>
<videos>
  <video>
    <title>Her Alibi</title>
    <director>Bruce Beresford</director>
    <length>94 Minutes</length>
    <format>DVD</format>
    <rating>PG-13</rating>
  </video>
  <video>
    <title>Day After Tomorrow(The)</title>
    <director>Roland Emmerich</director>
    <year>2004</year>
    <length>124</length>
    <format>DVD</format>
    <rating>PG-13</rating>
  </video>
</videos>

On the other hand, the XmlNode class is equipped with a method named ReplaceChild. Its syntax is:

public virtual XmlNode ReplaceChild(XmlNode newChild, XmlNode oldChild);

To use this method, first locate an element and get its reference. Then change the values or child nodes you want, and finally replace the original value with the new version. In reality, and as its name implies, it is not the primary purpose of this method to edit or update an element. The role of this method is to use one node in place of another.

Deleting Elements

Deleting an Element

If you have a node you don't want or don't need anymore in the document, you can delete it. To let you delete a node, the XmlNode class is equipped with a method named RemoveChild. Its syntax is:

public virtual XmlNode RemoveChild(XmlNode oldChild);

This method takes as argument the node to delete. If the node exists, it would be deleted and the method would return the node that was deleted. If the node does not exist, nothing would happen. To effectively use this method, you should first locate the particular node you want to delete. You can look for it using any of the techniques we have applied so far. Once you find the node, you can then delete it. Imagine you want to delete a node whose name is Director and whose value is Bruce Beresford. Here is an example of calling this method to perform the operation:

using System.IO;
using System.Xml;

public class Exercise
{
    public static int Main(string[] args)
    {
        string strVideosFile = @"C:\Videos Collection\Videos.xml";
        XmlDocument xdVideos = new XmlDocument();

        if (File.Exists(strVideosFile))
        {
            xdVideos.Load(strVideosFile);

            // Get a reference to the root node
            XmlElement xeRoot = xdVideos.DocumentElement;

            // Create a list of the videos
            XmlNodeList xnlVideos = xdVideos.GetElementsByTagName("video");

            // visit each video
            foreach (XmlNode node in xnlVideos)
            {
                // Within a video, get a list of its children
                XmlNodeList xnlChildren = node.ChildNodes;

                // Visit each child node
                foreach (XmlNode dir in xnlChildren)
                {
                    // If the child node is Bruce Beresford
                    if (dir.InnerText == "Bruce Beresford")
                    {
                        node.RemoveChild(dir);

                        // Save the file
                        xdVideos.Save(strVideosFile);

                        // Stop
                        break;
                    }
                }
            }
        }

        return 20_2020;
    }
}

Clearing an Element of its Children

To let you delete all child nodes of a node, the XmlNode class provides a method named RemoveAll. Its syntax is:

public virtual void RemoveAll();

When called, this method will remove all child nodes, if any, of their parent node. Here is an example of calling it:

using System.IO;
using System.Xml;

public class Exercise
{
    public static int Main(string[] args)
    {
        string strVideosFile = @"C:\Videos Collection\Videos.xml";
        XmlDocument xdVideos = new XmlDocument();

        if (File.Exists(strVideosFile))
        {
            // Open the XML file
            xdVideos.Load(strVideosFile);
            // Clear the XML document
            xdVideos.DocumentElement.RemoveAll();
            // Save the XML document
            xdVideos.Save(strVideosFile);
        }

        return 353_454;
    }
}

This would produce:

<?xml version="1.0" encoding="utf-8"?>
<videos>
</videos>

Practical Learning: Creating the Water Distribution Company Application

Start Microsoft Visual Studio and create a Windows Forms application named WaterDistributionCompany1
To create a new file, on the main menu, click Project -> Add New Item...
In the left list under Visual C# Items, click Data and, in the middle list, click Xml File
Change the file name to WaterMeters
Click Add

Change the document as follows:

<?xml version="1.0" encoding="utf-8" ?>
<water-meters>
	<water-meter>
		<meter-number>392-44-572</meter-number>
		<make>Constance Technologies</make>
		<model>TG-4822</model>
		<meter-size>5/8 Inches</meter-size>
	</water-meter>
	<water-meter>
		<meter-number>938-75-869</meter-number>
		<make>Stanford Trend</make>
		<model>266G</model>
		<meter-size>1 1/2 Inches</meter-size>
	</water-meter>
	<water-meter>
		<meter-number>799-28-461</meter-number>
		<make>Constance Technologies</make>
		<model>BD-7000</model>
		<meter-size>3/4 Inches</meter-size>
	</water-meter>
	<water-meter>
		<meter-number>207-94-835</meter-number>
		<make>Constance Technologies</make>
		<model>TG-6220</model>
		<meter-size>5/8 Inches</meter-size>
	</water-meter>
	<water-meter>
		<meter-number>592-84-957</meter-number>
		<make>Standard Trend</make>
		<model>428T</model>
		<meter-size>1 Inch3/4 Inches</meter-size>
	</water-meter>
	<water-meter>
		<meter-number>374-06-284</meter-number>
		<make>Raynes Energica</make>
		<model>i2022</model>
		<meter-size>3/4 Inches</meter-size>
	</water-meter>
</water-meters>

In the Solution Explorer, right-click WaterDistributionCompany1 -> Add -> Form (Windows Forms)...
Change the file name to WaterMeters as the name of the form
Click Add

Design the form as follows:

Control	(Name)	Text	Other Properties
ListView	lvwWaterMeters		FullRowSelect: True GridLines: True Anchor: Top, Bottom, Left, Right
Button	btnClose	Close	Anchor: Bottom, Right

List View Columns

(Name)	Text	TextAlign	Width
colNumber	#		20
colMeterNumber	Meter Number	Center	80
colMake	Make		110
colModel	Model		80
colMeterSize	Meter Size	Center	80

Double-click an unoccupied area of the form to launch its Load event
Return to the form and double-click the Close button

Change the document as follows:

using System;
using System.IO;
using System.Xml;
using System.Windows.Forms;

namespace WaterDistributionCompany1
{
    public partial class WaterMeters : Form
    {
        public WaterMeters()
        {
            InitializeComponent();
        }

        private void WaterMeters_Load(object sender, EventArgs e)
        {
            // Create a DOM object that will give access to the XML
            XmlDocument xdWaterMeters = new XmlDocument();
            // Specify the name of the file that contains the water meters records
            string strWaterMeters = "../../WaterMeters.xml";

            // Find out whether a file for water meters was already created.
            if (File.Exists(strWaterMeters))
            {
                // If that file exists, create a file stream to hold the file, and open it
                using (FileStream fsWaterMeters = new FileStream(strWaterMeters, FileMode.Open,
                                                                 FileAccess.Read, FileShare.Read))
                {
                    // Load the XML elements from the file to the DOM object
                    xdWaterMeters.Load(fsWaterMeters);
                    // Get a collection of the XML elements from the DOM object
                    XmlNodeList xnlWaterMeters = xdWaterMeters.DocumentElement.ChildNodes;

                    // This small integer will simpoly be used to count the number of water meters
                    int i = 1;

                    // Just in case the list view was displaying something, remove those things
                    lvwWaterMeters.Items.Clear();

                    // Visit each record from the collection of water meters
                    foreach (XmlNode xnWaterMeter in xnlWaterMeters)
                    {
                        /* Create list view item. Get it ready to display the 
                         * ordered number of the water meter. The number starts at 1. */
                        ListViewItem lviWaterMeter = new ListViewItem(i.ToString());

                        /* Create each child node from each water meter record and add it as a child 
                         * of the list view item (so it can be displayed in the appropriate colum). */
                        lviWaterMeter.SubItems.Add(xnWaterMeter.FirstChild.InnerText);
                        lviWaterMeter.SubItems.Add(xnWaterMeter.FirstChild.NextSibling.InnerText);
                        lviWaterMeter.SubItems.Add(xnWaterMeter.FirstChild.NextSibling.NextSibling.InnerText);
                        lviWaterMeter.SubItems.Add(xnWaterMeter.FirstChild.NextSibling.NextSibling.NextSibling.InnerText);

                        // Add the list view item to the list view (so it can be displayed in the appropriate colum).
                        lvwWaterMeters.Items.Add(lviWaterMeter);
                        // Increase the counter of the water meters
                        i++;
                    }
                } // Close the stream
            }
        }

        private void btnClose_Click(object sender, EventArgs e)
        {
            // Close the form
            this.Close();
        }
    }
}

To create a new form, in the Solution Explorer, right-click WaterDistributionCompany1 -> Add -> Form (Windows Forms)...
Change the file Name to CustomerNew
Click Add

Design the form as follows:

Control	(Name)	Text
Label		Account #:
TextBox	txtAccountNumber
Label		Meter #:
TextBox	txtMeterNumber
Label		Meter Details:
TextBox	txtMeterDetails
Label		First Name:
TextBox	txtFirstName
Label		Last Name:
TextBox	txtLastName
Label		Address:
TextBox	txtAddress
Label		City:
TextBox	txtCity
Label		County:
TextBox	txtCounty
Label		State:
TextBox	txtState
Label		ZIP Code:
TextBox	txtZIPCode
Button	btnSave	Save
Button	btnClose	Close

On the form, click the Meter # text box
In the Properties window, click the Events button
Double-click Leave
Return to the form and double-click the Save button
Return to the form and double-click the Close button

Change the document as follows:

using System;
using System.IO;
using System.Xml;
using System.Windows.Forms;

namespace WaterDistributionCompany1
{
    public partial class CustomerNew : Form
    {
        public CustomerNew()
        {
            InitializeComponent();
        }

        private void txtMeterNumber_Leave(object sender, EventArgs e)
        {
            XmlDocument xdWaterMeters = new XmlDocument();
            string strFileWaterMeters = "../../WaterMeters.xml";

            // The user must provide a valid meter number.
            // To start, find out if a file for water meters was created already.
            if (File.Exists(strFileWaterMeters))
            {
                // If a file for water meters exists, open it
                using (FileStream fsWaterMeters = new FileStream(strFileWaterMeters, FileMode.Open,
                                                                 FileAccess.Read, FileShare.Read))
                {
                    // Store the list of water meters in an XML document
                    xdWaterMeters.Load(fsWaterMeters);

                    // Create a list of child nodes of the root node
                    XmlNodeList xnlWaterMeters = xdWaterMeters.DocumentElement.ChildNodes;

                    // Visit each node of the list of elements
                    foreach (XmlNode xnWaterMeter in xnlWaterMeters)
                    {
                        // When you get to a list of nodes, create a list of its children and visit each
                        foreach (XmlNode xnMeterNumber in xnWaterMeter.ChildNodes)
                        {
                            // If you find a meter number that is the same as the meter number from the form, ...
                            if (xnMeterNumber.InnerText == txtMeterNumber.Text)
                            {
                                // ... display its details
                                txtMeterDetails.Text = xnMeterNumber.NextSibling.InnerText + " " +
                                                       xnMeterNumber.NextSibling.NextSibling.InnerText + 
                                                       " (Meter #: " + txtMeterNumber.Text + ")";
                            }
                        }
                    }
                }
            }
        }

        private void btnSaveCustomer_Click(object sender, EventArgs e)
        {
            // If the user didn't provide an account number, don't proceed any further
            if (string.IsNullOrEmpty(txtAccountNumber.Text))
            {
                MessageBox.Show("You must enter a new unique account number of the customer.",
                                "Water Distribution Company");
                return;
            }

            // If the user didn't provide an account number, ...
            if (string.IsNullOrEmpty(txtMeterNumber.Text))
            {
                MessageBox.Show("You must provide a valid meter number.",
                                "Water Distribution Company");
                return;
            }

            XmlDocument xdCustomersAccounts = new XmlDocument();
            string strCustomers = "../../Customers.xml";

            // It appears that the user provided both an account number and a valid meter number.
            // If an XML file for customers accounts was previously created, ...
            if (File.Exists(strCustomers))
            {
                // ... open it ...
                using (FileStream fsCustomers = new FileStream(strCustomers, FileMode.OpenOrCreate,
                                                               FileAccess.ReadWrite, FileShare.ReadWrite))
                {
                    // ... and put the records in the DOM
                    xdCustomersAccounts.Load(fsCustomers);
                }
            }
            else
            {
                // If there no XML file yet for the customers, create skeleton code for an XML document
                xdCustomersAccounts.LoadXml("<?xml version=\"1.0\" encoding=\"utf-8\"?>" +
                                            "<customers></customers>");
            }

            // Get ready to create an XML element named customer
            XmlElement xeCustomer = xdCustomersAccounts.CreateElement("customer");

            // Create the markup of the XML customer
            string strCustomer = "<account-number>" + txtAccountNumber.Text + "</account-number>" +
                                 "<meter-number>"   + txtMeterNumber.Text   + "</meter-number>"   +
                                 "<first-name>"     + txtFirstName.Text     + "</first-name>"     +
                                 "<last-name>"      + txtLastName.Text      + "</last-name>"      +
                                 "<address>"        + txtAddress.Text       + "</address>"        +
                                 "<city>"           + txtCity.Text          + "</city>"           +
                                 "<county>"         + txtCounty.Text        + "</county>"         +
                                 "<state>"          + txtState.Text         + "</state>"          +
                                 "<zip-code>"       + txtZIPCode.Text       + "</zip-code>";

            // Specify the markup of the new element
            xeCustomer.InnerXml = strCustomer;

            // Add the new node to the root
            xdCustomersAccounts.DocumentElement.PrependChild(xeCustomer);

            // Save the (new version of the) XML file
            using (FileStream fsCustomers = new FileStream(strCustomers, FileMode.Create, FileAccess.Write, FileShare.Write))
            {
                xdCustomersAccounts.Save(fsCustomers);
            }

            Close();
        }

        private void btnClose_Click(object sender, EventArgs e)
        {
            Close();
        }
    }
}

To create a new form, in the Solution Explorer, right-click WaterDistributionCompany1 -> Add -> Form (Windows Forms)...
Change the file name to CustomerEditor
Click Add

Design the form as follows:

Control	(Name)	Text
Label		Account #:
TextBox	txtAccountNumber
Button	btnOpen	Open
Label		Meter #:
TextBox	txtMeterNumber
Label		Meter Details:
TextBox	txtMeterDetails
Label		First Name:
TextBox	txtFirstName
Label		Last Name:
TextBox	txtLastName
Label		Address:
TextBox	txtAddress
Label		City:
TextBox	txtCity
Label		County:
TextBox	txtCounty
Label		State:
TextBox	txtState
Label		ZIP Code:
TextBox	txtZIPCode
Button	btnUpdateWaterMeter	Save/Update Water Meter
Button	btnClose	Close

In the Properties window, click the Events button
On the form, click the Meter # text box
Double-click Leave
Return to the form and double-click the Open button
Return to the form and double-click the Save/Update Water Meter button
Return to the form and double-click the Close button

Change the document as follows:

using System;
using System.IO;
using System.Windows.Forms;
using System.Xml;

namespace WaterDistributionCompany1
{
    public partial class CustomerEditor : Form
    {
        public CustomerEditor()
        {
            InitializeComponent();
        }

        void FindWaterMeter()
        {
            if( string.IsNullOrEmpty(txtMeterNumber.Text))
                return;

            XmlDocument xdWaterMeters = new XmlDocument();
            string strFileWaterMeters = "../../WaterMeters.xml";

            /* This code will run if the user had first put a valid account number; then this 
             * code is used to find the water meter associated with the customer's account. */
            if (File.Exists(strFileWaterMeters))
            {
                // Open the file that contains the water meter details
                using (FileStream fsWaterMeters = new FileStream(strFileWaterMeters, FileMode.Open,
                                                                 FileAccess.Read, FileShare.Read))
                {
                    // Store the list of water meters in an XML DOM
                    xdWaterMeters.Load(fsWaterMeters);

                    // Create a list of elements based on a node named meter-number
                    XmlNodeList xnlWaterMeters = xdWaterMeters.DocumentElement.GetElementsByTagName("meter-number");

                    // Visit each node of the list of elements
                    foreach (XmlNode xnWaterMeter in xnlWaterMeters)
                    {
                        // If you find a meter number that is the same as the meter number from the form, ...
                        if(xnWaterMeter.InnerText == txtMeterNumber.Text)   
                        {
                            // ... display its details
                            txtMeterDetails.Text = xnWaterMeter.NextSibling.InnerText + " " + xnWaterMeter.NextSibling.NextSibling.InnerText + " (Meter #: " + txtMeterNumber.Text + ")";
                        }
                    }
                }
            }
        }

        private void txtMeterNumber_Leave(object sender, EventArgs e)
        {
            FindWaterMeter();
        }

        private void btnOpen_Click(object sender, EventArgs e)
        {
            XmlDocument xdCustomers = new XmlDocument();
            string strCustomers = "../../Customers.xml";
            FileInfo fiCustomers = new FileInfo(strCustomers);

            if( fiCustomers.Exists == true )
            {
                using (FileStream fsCustomers = new FileStream(fiCustomers.FullName, FileMode.Open,
                                                               FileAccess.Read, FileShare.Read))
                {
                    xdCustomers.Load(fsCustomers);

                    XmlNodeList xnlCustomers = xdCustomers.DocumentElement.GetElementsByTagName("account-number");

                    foreach (XmlNode xnCustomer in xnlCustomers)
                    {
                        if( xnCustomer.InnerText == txtAccountNumber.Text)
                        {
                            txtMeterNumber.Text = xnCustomer.NextSibling.InnerText;
                            txtFirstName.Text   = xnCustomer.NextSibling.NextSibling.InnerText;
                            txtLastName.Text    = xnCustomer.NextSibling.NextSibling.NextSibling.InnerText;
                            txtAddress.Text     = xnCustomer.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                            txtCity.Text        = xnCustomer.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                            txtCounty.Text      = xnCustomer.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                            txtState.Text       = xnCustomer.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                            txtZIPCode.Text     = xnCustomer.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;

                            break;
                        }
                    }
                }
            }

            FindWaterMeter();
        }

        private void btnSave_Click(object sender, EventArgs e)
        {
            if (string.IsNullOrEmpty(txtAccountNumber.Text))
                return;

            if (string.IsNullOrEmpty(txtMeterNumber.Text))
                return;

            XmlNode xnExisting = null;

            XmlDocument xdCustomers = new XmlDocument();
            string strCustomers = "../../Customers.xml";
            FileInfo fiCustomers = new FileInfo(strCustomers);

            if (fiCustomers.Exists == true)
            {
                using (FileStream fsCustomers = new FileStream(fiCustomers.FullName, FileMode.Open,
                                                               FileAccess.Read, FileShare.Read))
                {
                    xdCustomers.Load(fsCustomers);

                    XmlNodeList xnlCustomers = xdCustomers.DocumentElement.ChildNodes;

                    foreach (XmlNode xnCustomer in xnlCustomers)
                    {
                        foreach (XmlNode xnAccountNumber in xnCustomer.ChildNodes)
                        {
                            if (xnAccountNumber.InnerText == txtAccountNumber.Text)
                            {
                                xnExisting = xnCustomer;
                                break;
                            }
                        }
                    }
                }
            }

            XmlElement xeUpdatedCustomer = xdCustomers.CreateElement("customer");
            
            string strUpdatedCustomer = "<account-number>" + txtAccountNumber.Text + "</account-number>" +
                                        "<meter-number>" + txtMeterNumber.Text + "</meter-number>" +
                                        "<first-name>" + txtFirstName.Text + "</first-name>" +
                                        "<last-name>" + txtLastName.Text + "</last-name>" +
                                        "<address>" + txtAddress.Text + "</address>" +
                                        "<city>" + txtCity.Text + "</city>" +
                                        "<county>" + txtCounty.Text + "</county>" +
                                        "<state>" + txtState.Text + "</state>" +
                                        "<zip-code>" + txtZIPCode.Text + "</zip-code>";
            
            xeUpdatedCustomer.InnerXml = strUpdatedCustomer;

            xdCustomers.DocumentElement.ReplaceChild(xeUpdatedCustomer, xnExisting);
            
            using (FileStream fsCustomers = new FileStream(fiCustomers.FullName, FileMode.OpenOrCreate, FileAccess.ReadWrite, FileShare.ReadWrite))
            {
                xdCustomers.Save(fsCustomers);    
            }
            
            Close();
        }

        private void btnClose_Click(object sender, EventArgs e)
        {
            Close();
        }
    }
}

To create another form, on the main menu, click Project -> Add New Form (Windows Forms)...
Change the file name to Customers
Click Add

Design the form as follows:

Control	(Name)	Text	Other Properties
ListView	lvwCustomers		FullRowSelect: True GridLines: True Anchor: Top, Bottom, Left, Right
Button	btnNewCustomer	New Customer	Anchor: Bottom, Right
Button	btnCustomerEditor	Customer Editor...	Anchor: Bottom, Right
Button	btnClose	Close	Anchor: Bottom, Right

List View Columns

(Name)	Text	TextAlign	Width
colNumber	#		20
colAccountNumber	Account #		90
colMeterNumber	Meter Number	Center	80
colFirstName	First Name		65
colLastName	Last Name		65
colAddress	Address		135
colCity	City		80
colCounty	County		80
colZIPCode	ZIP Code

Double-click an unoccupied area of the form to generate its Load event
Return to the form and double-click the New Customer button
Return to the form and double-click the Customer Editor button
Return to the form and double-click the Close button

Change the document as follows:

using System;
using System.IO;
using System.Xml;
using System.Windows.Forms;

namespace WaterDistributionCompany1
{
    public partial class Customers : Form
    {
        public Customers()
        {
            InitializeComponent();
        }

        private void Customers_Load(object sender, EventArgs e)
        {
            XmlDocument xdCustomers = new XmlDocument();
            string strCustomers = "../../Customers.xml";
            FileInfo fiCustomers = new FileInfo(strCustomers);

            if( File.Exists(strCustomers))
            {
                // ... open that file
                using( FileStream fsCustomers = new FileStream(strCustomers, FileMode.Open,
                                                               FileAccess.Read, FileShare.Read) )
                {
                    // Get the list of customers from the file and put that list in our initial empty list of customers
                    xdCustomers.Load(fsCustomers);

                    /* Since it appears that we currently have a list of customers, let's find out if
                     * it contains a customer with the account number that was entered in the form. */
                    XmlNodeList xnlCustomers = xdCustomers.DocumentElement.ChildNodes;

                    int i = 1;

                    lvwCustomers.Items.Clear();

                    // Visit each node of the list of elements
                    foreach (XmlNode xnCustomer in xnlCustomers)
                    {
                        ListViewItem lviCustomer = new ListViewItem(i.ToString());

                        lviCustomer.SubItems.Add(xnCustomer.FirstChild.InnerText);
                        lviCustomer.SubItems.Add(xnCustomer.FirstChild.NextSibling.InnerText);
                        lviCustomer.SubItems.Add(xnCustomer.FirstChild.NextSibling.NextSibling.InnerText);
                        lviCustomer.SubItems.Add(xnCustomer.FirstChild.NextSibling.NextSibling.NextSibling.InnerText);
                        lviCustomer.SubItems.Add(xnCustomer.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.InnerText);
                        lviCustomer.SubItems.Add(xnCustomer.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText);
                        lviCustomer.SubItems.Add(xnCustomer.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText);
                        lviCustomer.SubItems.Add(xnCustomer.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText);

                        lvwCustomers.Items.Add(lviCustomer);
                        i++;
                    }
                } // Using
            }
        }

        private void btnNewCustomer_Click(object sender, EventArgs e)
        {
            CustomerNew cn = new CustomerNew();

            cn.ShowDialog();

            Customers_Load(sender, e);
        }

        private void btnCustomerEditor_Click(object sender, EventArgs e)
        {
            CustomerEditor ce = new CustomerEditor();

            ce.ShowDialog();

            Customers_Load(sender, e);
        }

        private void btnClose_Click(object sender, EventArgs e)
        {
            Close();
        }
    }
}

To create a new form, in the Solution Explorer, right-click WaterDistributionCompany -> Add -> Form (Windows Forms)...
Change the file Name to BillPreparation
Click Add
To create a new form, on the main menu, click Project -> Add Form (Windows Forms)...
Change the file name to BillEditor
Click Add
Click the BillPreparation.cs [Design] tab to return to the Bill Preparation form

Design the form as follows:

Control	(Name)	Text	Other Properties
Label		Customer Account Information	Font: Georgia, 9.75pt, style=Bold, Italic
Label		Account #:
TextBox	txtAccountNumber
Label		Customer Name:
TextBox	txtCustomerName
TextBox	txtAddress
TextBox	txtCity
TextBox:	txtCounty
TextBox	txtState
TextBox	txtZIPCode
Label		Meter Information	Georgia, 9.75pt, style=Bold, Italic
Label		Meter Details:
TextBox	txtMeterNumber
TextBox	txtMeterDetails
Label		Meter Reading
Label		___________________
Label		Service Start Date:
DateTimeIcker	dtpServiceStartDate		Format: Short
Label		Service End Date:
DateTimeIcker	dtpServiceEndDate		Format: Short
Label		Number of Days:
TextBox	txtNumberOfDays		TextAlign: Right
Label		Counter Readiing Start:
TextBox	txtCounterReadiingStart		TextAlign: Right
Label		Counter Readiing End:
TextBox	txtCounterReadiingEnd		TextAlign: Right
Label		Total HCF:
TextBox	txtTotalHCF		TextAlign: Right
Label		Total Gal1ons:
TextBox	txtTotalGallons		TextAlign: Right
Label		1st 15 HCF at $3.6121:
TextBox	txtFirst15HCF		TextAlign: Right
Label		Next 10 HCF at $3.9180:
TextBox	txtNext10HCF		TextAlign: Right
Label		Remaining HCF at $4.2763:
TextBox	txtRemainingHCF		TextAlign: Right
Label		Sewer Charges:
TextBox	txtSewerCharges		TextAlign: Right
Label		Storm Charges:
TextBox	txtStormCharges		TextAlign: Right
Label		Water Usage Charges
TextBox	txtWaterUsageCharges		TextAlign: Right
Label	Total Charges:
TextBox	txtTotalCharges		RightAlign: Right
Label		Water Bill Values	Font: Georgia, 9.75pt, style=Bold, Italic
Label		Local/County Taxes:
TextBox	txtLocalTaxes
Label		State Taxes:
TextBox	txtStateTaxes
Label		_________________________
Label		Payment Due Date:
TextBox	txtPaymentDueDate		TextAlign: Right
Label		Amount Due:
TextBox	txtAmountDue		TextAlign: Right
Label		Late Payment Due Date:
TextBox	txtLatePaymentDueDate		TextAlign: Right
Label		Late Payment Amount Due:
TextBox	txtLatePaymentAmountDue		TextAlign: Right
Label		_________________________
Label		Water Bill #:
TextBox	txtBillNumber		TextAlign: Right
Button	btnSaveWaterBill	Save Water Bill
Button	btnReviewWaterBill	Review Water Bill...
Button	btnClose	Close

Double-click an unoccupied area of the form to access its Load event
Return to the form and click the Account # text box
In the Properties window, click the Events button
In the Events section of the Properties window, double-click Leave
Return to the form and double-click the Service Start Date date time picker
Return to the form and double-click the Service End Date date time picker
Return to the form and click the Counter Reading End text box
In the Events section of the Properties window, double-click Leave
Return to the form and double-click the Save Water Bill button
Return to the form and double-click the Review Water Bill button
Return to the form and double-click the Close button

Change the document as follows:

using System;
using System.IO;
using System.Xml;
using System.Windows.Forms;

namespace WaterDistributionCompany1
{
    public partial class BillPreparation : Form
    {
        public BillPreparation()
        {
            InitializeComponent();
        }

        private void BillPreparation_Load(object sender, EventArgs e)
        {
            Random rndNumber = new Random();

            txtBillNumber.Text = rndNumber.Next(100001, 999999).ToString();
        }

        void IdentifyCustomer()
        {
            if (string.IsNullOrEmpty(txtAccountNumber.Text))
                return;

            XmlDocument xdCustomers = new XmlDocument();
            FileInfo fiCustomers = new FileInfo("../../Customers.xml");

            // The user must provide a valid account meter.
            // To start, find out if a file for customers accounts exists already.
            if( fiCustomers.Exists == true )
            {
                // If a file for water meters exists, open it
                using (FileStream fsCustomers = new FileStream(fiCustomers.FullName, FileMode.Open,
                                                                 FileAccess.Read, FileShare.Read))
                {
                    // Store the list of customers in an XML DOM
                    xdCustomers.Load(fsCustomers);

                    // Create a list of child nodes of the root node
                    XmlNodeList xnlCustomers = xdCustomers.DocumentElement.ChildNodes;

                    // Visit each node of the list of elements
                    foreach (XmlNode xnCustomer in xnlCustomers)
                    {
                        // When you get to a list of nodes, create a list of its children and visit each
                        foreach (XmlNode xnAccountNumber in xnCustomer.ChildNodes)
                        {
                            // If you find a customer whose account number is the same as the account number the user typed, ...
                            if (xnAccountNumber.InnerText == txtAccountNumber.Text)
                            {
                                // ... display its details
                                txtMeterNumber.Text = xnAccountNumber.NextSibling.InnerText;
                                txtCustomerName.Text = xnAccountNumber.NextSibling.NextSibling.InnerText + " " + xnAccountNumber.NextSibling.NextSibling.NextSibling.InnerText;
                                txtAddress.Text      = xnAccountNumber.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                                txtCity.Text         = xnAccountNumber.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                                txtCounty.Text       = xnAccountNumber.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                                txtState.Text        = xnAccountNumber.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                                txtZIPCode.Text      = xnAccountNumber.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                            }
                        }
                    }
                }
            }
        }

        void IdentifyWaterMeter()
        {
            IdentifyCustomer();

            if( string.IsNullOrEmpty(txtMeterNumber.Text) )
                return;

            XmlDocument xdWaterMeters = new XmlDocument();
            string strFileWaterMeters = "../../WaterMeters.xml";

            if (File.Exists(strFileWaterMeters))
            {
                using (FileStream fsWaterMeters = new FileStream(strFileWaterMeters, FileMode.Open,
                                                                 FileAccess.Read, FileShare.Read))
                {
                    xdWaterMeters.Load(fsWaterMeters);

                    XmlNodeList xnlWaterMeters = xdWaterMeters.DocumentElement.ChildNodes;

                    foreach (XmlNode xnWaterMeter in xnlWaterMeters)
                    {
                        foreach (XmlNode xnMeterNumber in xnWaterMeter.ChildNodes)
                        {
                            if (xnMeterNumber.InnerText == txtMeterNumber.Text)
                            {
                                txtMeterDetails.Text = xnMeterNumber.NextSibling.InnerText + " " + xnMeterNumber.NextSibling.NextSibling.InnerText + " (Meter #: " + txtMeterNumber.Text + ")";
                                break;
                            }
                        }
                    }
                }
            }
        }

        private void txtAccountNumber_Leave(object sender, EventArgs e)
        {
            IdentifyWaterMeter();
        }

        private void dtpServiceStartDate_ValueChanged(object sender, EventArgs e)
        {
            DateTime dtStart = dtpServiceStartDate.Value;
            DateTime dtEnd = dtpServiceEndDate.Value;
            TimeSpan tsDays = dtEnd.Subtract(dtStart);

            txtNumberOfDays.Text = tsDays.Days.ToString();

            txtPaymentDueDate.Text = dtpServiceEndDate.Value.AddDays(28).ToShortDateString();
            txtLatePaymentDueDate.Text = dtpServiceEndDate.Value.AddDays(45).ToShortDateString();
        }

        private void dtpServiceEndDate_ValueChanged(object sender, EventArgs e)
        {
            dtpServiceStartDate_ValueChanged(sender, e);
        }

        private void txtCounterReadingEnd_Leave(object sender, EventArgs e)
        {
            /* Let's compute the numbers for the water bill.
             * The following calculations are not based on anything real.
             * I used my own rough estimates with weird non-extensive research based on nothing.
             * These calculations are for demonstration purposes only for our lesson. */
            double next10HCF;
            double first15HCF;
            double remainingHCF;

            double counterReadingStart = double.Parse(txtCounterReadingStart.Text);
            double counterReadingEnd = double.Parse(txtCounterReadingEnd.Text);

            double totalHCF = counterReadingEnd - counterReadingStart;
            int totalGallons = (int)(totalHCF * 748.05);

            if (totalHCF <= 15)
            {
                first15HCF = totalHCF * 3.612;
                next10HCF = 0;
                remainingHCF = 0;
            }
            else if (totalHCF <= 25)
            {
                first15HCF = 15 * 3.612;
                next10HCF = (totalHCF - 15) * 3.918;
                remainingHCF = 0;
            }
            else
            {
                first15HCF = 15 * 3.612;
                next10HCF = 10 * 3.918;
                remainingHCF = (totalHCF - 25) * 2.2763;
            }

            double waterUsageCharge = first15HCF + next10HCF + remainingHCF;
            double sewerCharge = waterUsageCharge * 0.252;
            double stormCharge = waterUsageCharge * 0.0025;
            double totalCharges = waterUsageCharge + sewerCharge + stormCharge;
            double countyTaxes = totalCharges * 0.005;
            double stateTaxes = totalCharges * 0.0152;
            double amountDue = totalCharges + countyTaxes + stateTaxes;

            txtTotalHCF.Text = totalHCF.ToString("F");
            txtNext10HCF.Text = next10HCF.ToString("F");
            txtAmountDue.Text = amountDue.ToString("F");
            txtStateTaxes.Text = stateTaxes.ToString("F");
            txtFirst15HCF.Text = first15HCF.ToString("F");
            txtSewerCharges.Text = sewerCharge.ToString("F");
            txtStormCharges.Text = stormCharge.ToString("F");
            txtLocalTaxes.Text = countyTaxes.ToString("F");
            txtTotalGallons.Text = totalGallons.ToString("F");
            txtRemainingHCF.Text = remainingHCF.ToString("F");
            txtTotalCharges.Text = totalCharges.ToString("F");
            txtLatePaymentAmountDue.Text = (amountDue + 8.95).ToString("F");
            txtWaterUsageCharges.Text = waterUsageCharge.ToString("F");
        }

        private void btnSaveWaterBill_Click(object sender, EventArgs e)
        {
            XmlDocument xdWaterBills = new XmlDocument();
            string strFileWaterBills = "../../WaterBills.xml";

            if( string.IsNullOrEmpty(txtBillNumber.Text) )
            {
                MessageBox.Show("You must enter an invoice/bill number.", "Water Distribution Company");
                return;
            }

            if (string.IsNullOrEmpty(txtAccountNumber.Text))
            {
                MessageBox.Show("You must specify the customer's account number.", "Water Distribution Company");
                return;
            }

            if (string.IsNullOrEmpty(txtMeterNumber.Text))
            {
                MessageBox.Show("You must enter a meter number.", "Water Distribution Company");
                return;
            }

            if (File.Exists(strFileWaterBills))
            {
                using (FileStream fsWaterBills = new FileStream(strFileWaterBills, FileMode.OpenOrCreate, FileAccess.ReadWrite, FileShare.ReadWrite))
                {
                    // ... and put the records in the DOM
                    xdWaterBills.Load(fsWaterBills);
                }
            }
            else
            {
                xdWaterBills.LoadXml("<?xml version=\"1.0\" encoding=\"utf-8\"?>" +
                                     "<water-bills></water-bills>");
            }
            
            XmlElement xeWaterBill = xdWaterBills.CreateElement("water-bill");
            
            xeWaterBill.InnerXml = "<bill-number>" + txtBillNumber.Text + "</bill-number>" +
                                   "<account-number>" + txtAccountNumber.Text + "</account-number>" +
                                   "<meter-reading-start-date>" + dtpServiceStartDate.Value.ToShortDateString() + "</meter-reading-start-date>" +
                                   "<meter-reading-end-date>" + dtpServiceEndDate.Value.ToShortDateString() + "</meter-reading-end-date>" +
                                   "<number-of-days>" + txtNumberOfDays.Text + "</number-of-days>" +
                                   "<counter-reading-start>" + txtCounterReadingStart.Text + "</counter-reading-start>" +
                                   "<counter-reading-end>" + txtCounterReadingEnd.Text + "</counter-reading-end>" +
                                   "<total-hcf>" + txtTotalHCF.Text + "</total-hcf>" +
                                   "<total-gallons>" + txtTotalGallons.Text + "</total-gallons>" +
                                   "<first-15-hcf>" + txtFirst15HCF.Text + "</first-15-hcf>" +
                                   "<next-10-hcf>" + txtNext10HCF.Text + "</next-10-hcf>" +
                                   "<remaining-hcf>" + txtRemainingHCF.Text + "</remaining-hcf>" +
                                   "<sewer-charges>" + txtSewerCharges.Text + "</sewer-charges>" +
                                   "<storm-charges>" + txtStormCharges.Text + "</storm-charges>" +
                                   "<water-usage-charges>" + txtWaterUsageCharges.Text + "</water-usage-charges>" +
                                   "<total-charges>" + txtTotalCharges.Text + "</total-charges>" +
                                   "<local-taxes>" + txtLocalTaxes.Text + "</local-taxes>" +
                                   "<state-taxes>" + txtStateTaxes.Text + "</state-taxes>" +
                                   "<payment-due-date>" + txtPaymentDueDate.Text + "</payment-due-date>" +
                                   "<amount-due>" + txtAmountDue.Text + "</amount-due>" +
                                   "<late-payment-due-date>" + txtLatePaymentDueDate.Text + "</late-payment-due-date>" +
                                   "<late-amount-due>" + txtLatePaymentAmountDue.Text + "</late-amount-due>";
            
            xdWaterBills.DocumentElement.PrependChild(xeWaterBill);
            
            using (FileStream fsWaterBills = new FileStream(strFileWaterBills, FileMode.Create, FileAccess.Write, FileShare.Write))
            {
                xdWaterBills.Save(fsWaterBills);
            }

            Close();
        }

        private void btnReviewWaterBill_Click(object sender, EventArgs e)
        {
            BillEditor be = new BillEditor();

            be.ShowDialog();
        }

        private void btnClose_Click(object sender, EventArgs e)
        {
            Close();
        }
    }
}

Click the BillEditor.cs [Design] tab to access its form

Design the form as follows:

Control	(Name)	Text	Other Properties
Label		Customer Account Information	Font: Georgia, 9.75pt, style=Bold, Italic
Label		Account #:
TextBox	txtAccountNumber
Label		Customer Name:
TextBox	txtCustomerName
TextBox	txtAddress
TextBox	txtCity
TextBox:	txtCounty
TextBox	txtState
TextBox	txtZIPCode
Label		Meter Information	Georgia, 9.75pt, style=Bold, Italic
Label		Meter Details:
TextBox	txtMeterNumber
TextBox	txtMeterDetails
Label		Meter Reading
Label		___________________
Label		Service Start Date:
DateTimeIcker	dtpServiceStartDate		Format: Short
Label		Service End Date:
DateTimeIcker	dtpServiceEndDate		Format: Short
Label		Number of Days:
TextBox	txtNumberOfDays		TextAlign: Right
Label		Counter Readiing Start:
TextBox	txtCounterReadiingStart		TextAlign: Right
Label		Counter Readiing End:
TextBox	txtCounterReadiingEnd		TextAlign: Right
Label		Total HCF:
TextBox	txtTotalHCF		TextAlign: Right
Label		Total Gal1ons:
TextBox	txtTotalGallons		TextAlign: Right
Label		1st 15 HCF at $3.6121:
TextBox	txtFirst15HCF		TextAlign: Right
Label		Next 10 HCF at $3.9180:
TextBox	txtNext10HCF		TextAlign: Right
Label		Remaining HCF at $4.2763:
TextBox	txtRemainingHCF		TextAlign: Right
Label		Sewer Charges:
TextBox	txtSewerCharges		TextAlign: Right
Label		Storm Charges:
TextBox	txtStormCharges		TextAlign: Right
Label		Water Usage Charges
TextBox	txtWaterUsageCharges		TextAlign: Right
Label	Total Charges:
TextBox	txtTotalCharges		RightAlign: Right
Label		Water Bill Values	Font: Georgia, 9.75pt, style=Bold, Italic
Label		Local/County Taxes:
TextBox	txtLocalTaxes		TextAlign: Right
Label		State Taxes:
TextBox	txtStateTaxes
Label		_________________________
Label		Payment Due Date:
TextBox	txtPaymentDueDate		TextAlign: Right
Label		Amount Due:
TextBox	txtAmountDue		TextAlign: Right
Label		Late Payment Due Date:
TextBox	txtLatePaymentDueDate		TextAlign: Right
Label		Late Payment Amount Due:
TextBox	txtLatePaymentAmountDue		TextAlign: Right
Label		_________________________
Label		Water Bill #:
TextBox	txtBillNumber		TextAlign: Right
Button	btnOpen	Open
Button	btnSaveWaterBill	Save Water Bill
Button	btnReviewWaterBill	Review Water Bill...
Button	btnClose	Close

On the form, double-click the Open button
Return to the form and click the Account # text box
In the Properties window, click the Events button
In the Events section of the Properties window, double-click Leave
Return to the form and double-click the Service Start Date date time picker
Return to the form and double-click the Service End Date date time picker
Return to the form and click the Counter Reading End text box
In the Events section of the Properties window, double-click Leave
Return to the form and double-click the Save Water Bill button
Return to the form and double-click the Review Water Bill button
Return to the form and double-click the Close button

Change the document as follows:

using System;
using System.IO;
using System.Xml;
using System.Windows.Forms;

namespace WaterDistributionCompany1
{
    public partial class BillEditor : Form
    {
        public BillEditor()
        {
            InitializeComponent();
        }

        void IdentifyCustomer()
        {
            if (string.IsNullOrEmpty(txtAccountNumber.Text))
                return;

            XmlDocument xdCustomers = new XmlDocument();
            FileInfo fiCustomers = new FileInfo("../../Customers.xml");

            if (fiCustomers.Exists == true)
            {
                // If a file for water meters exists, open it
                using (FileStream fsCustomers = new FileStream(fiCustomers.FullName, FileMode.Open,
                                                                 FileAccess.Read, FileShare.Read))
                {
                    // Store the list of customers in an XML DOM
                    xdCustomers.Load(fsCustomers);

                    // Create a list of child nodes of the root node
                    XmlNodeList xnlCustomers = xdCustomers.DocumentElement.ChildNodes;

                    // Visit each node of the list of elements
                    foreach (XmlNode xnCustomer in xnlCustomers)
                    {
                        // When you get to a list of nodes, create a list of its children and visit each
                        foreach (XmlNode xnAccountNumber in xnCustomer.ChildNodes)
                        {
                            // If you find a customer whose account number is the same as the account number the user typed, ...
                            if (xnAccountNumber.InnerText == txtAccountNumber.Text)
                            {
                                // ... display its details
                                txtMeterNumber.Text  = xnAccountNumber.NextSibling.InnerText;
                                txtCustomerName.Text = xnAccountNumber.NextSibling.NextSibling.InnerText + " " +
                                                       xnAccountNumber.NextSibling.NextSibling.NextSibling.InnerText;
                                txtAddress.Text      = xnAccountNumber.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                                txtCity.Text         = xnAccountNumber.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                                txtCounty.Text       = xnAccountNumber.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                                txtState.Text        = xnAccountNumber.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                                txtZIPCode.Text      = xnAccountNumber.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                            }
                        }
                    }
                }
            }
        }

        void IdentifyWaterMeter()
        {
            if (string.IsNullOrEmpty(txtAccountNumber.Text))
                return;

            IdentifyCustomer();

            if (string.IsNullOrEmpty(txtMeterNumber.Text))
                return;

            XmlDocument xdWaterMeters = new XmlDocument();
            string strFileWaterMeters = "../../WaterMeters.xml";

            if (File.Exists(strFileWaterMeters))
            {
                using (FileStream fsWaterMeters = new FileStream(strFileWaterMeters, FileMode.Open,
                                                                 FileAccess.Read, FileShare.Read))
                {
                    xdWaterMeters.Load(fsWaterMeters);

                    XmlNodeList xnlWaterMeters = xdWaterMeters.DocumentElement.ChildNodes;

                    foreach (XmlNode xnWaterMeter in xnlWaterMeters)
                    {
                        foreach (XmlNode xnMeterNumber in xnWaterMeter.ChildNodes)
                        {
                            if (xnMeterNumber.InnerText == txtMeterNumber.Text)
                            {
                                txtMeterDetails.Text = xnMeterNumber.NextSibling.InnerText + " " + 
                                                       xnMeterNumber.NextSibling.NextSibling.InnerText +
                                                       " (Meter #: " + txtMeterNumber.Text + ")";
                                break;
                            }
                        }
                    }
                }
            }
        }

        private void btnOpen_Click(object sender, EventArgs e)
        {
            XmlDocument xdWaterBills = new XmlDocument();
            FileInfo fiWaterBills = new FileInfo("../../WaterBills.xml");

            if (fiWaterBills.Exists == true)
            {
                using (FileStream fsWaterBills = new FileStream(fiWaterBills.FullName, FileMode.Open,
                                                                FileAccess.Read, FileShare.Read))
                {
                    xdWaterBills.Load(fsWaterBills);

                    XmlNodeList xnlWaterBills = xdWaterBills.DocumentElement.ChildNodes;

                    foreach (XmlNode xnWaterBill in xnlWaterBills)
                    {
                        foreach (XmlNode xnBillNumber in xnWaterBill.ChildNodes)
                        {
                            if (xnBillNumber.InnerText == txtBillNumber.Text)
                            {
                                txtAccountNumber.Text        =                xnBillNumber.NextSibling.InnerText;
                                dtpServiceStartDate.Value    = DateTime.Parse(xnBillNumber.NextSibling.NextSibling.InnerText);
                                dtpServiceEndDate.Value      = DateTime.Parse(xnBillNumber.NextSibling.NextSibling.NextSibling.InnerText);
                                txtNumberOfDays.Text         =                xnBillNumber.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                                txtCounterReadingStart.Text  =                xnBillNumber.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                                txtCounterReadingEnd.Text    =                xnBillNumber.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                                txtTotalHCF.Text             =                xnBillNumber.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                                txtTotalGallons.Text         =                xnBillNumber.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                                txtFirst15HCF.Text           =                xnBillNumber.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                                txtNext10HCF.Text            =                xnBillNumber.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                                txtRemainingHCF.Text         =                xnBillNumber.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                                txtSewerCharges.Text         =                xnBillNumber.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                                txtStormCharges.Text         =                xnBillNumber.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                                txtWaterUsageCharges.Text    =                xnBillNumber.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                                txtTotalCharges.Text         =                xnBillNumber.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                                txtLocalTaxes.Text           =                xnBillNumber.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                                txtStateTaxes.Text           =                xnBillNumber.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                                txtPaymentDueDate.Text       =                xnBillNumber.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                                txtAmountDue.Text            =                xnBillNumber.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                                txtLatePaymentDueDate.Text   =                xnBillNumber.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                                txtLatePaymentAmountDue.Text =                xnBillNumber.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                            }
                        }
                    }
                }
            }

            IdentifyWaterMeter();
        }

        private void txtAccountNumber_Leave(object sender, EventArgs e)
        {
            IdentifyWaterMeter();
        }

        private void dtpServiceStartDate_ValueChanged(object sender, EventArgs e)
        {
            DateTime dtStart = dtpServiceStartDate.Value;
            DateTime dtEnd = dtpServiceEndDate.Value;
            TimeSpan tsDays = dtEnd.Subtract(dtStart);

            txtNumberOfDays.Text = tsDays.Days.ToString();

            txtPaymentDueDate.Text = dtpServiceEndDate.Value.AddDays(28).ToShortDateString();
            txtLatePaymentDueDate.Text = dtpServiceEndDate.Value.AddDays(45).ToShortDateString();
        }

        private void dtpServiceEndDate_ValueChanged(object sender, EventArgs e)
        {
            dtpServiceStartDate_ValueChanged(sender, e);
        }

        private void txtCounterReadingEnd_Leave(object sender, EventArgs e)
        {
            double next10HCF;
            double first15HCF;
            double remainingHCF;

            double counterReadingStart = double.Parse(txtCounterReadingStart.Text);
            double counterReadingEnd = double.Parse(txtCounterReadingEnd.Text);

            double totalHCF = counterReadingEnd - counterReadingStart;
            int totalGallons = (int)(totalHCF * 748.05);

            if (totalHCF <= 15)
            {
                first15HCF = totalHCF * 3.612;
                next10HCF = 0;
                remainingHCF = 0;
            }
            else if (totalHCF <= 25)
            {
                first15HCF = 15 * 3.612;
                next10HCF = (totalHCF - 15) * 3.918;
                remainingHCF = 0;
            }
            else
            {
                first15HCF = 15 * 3.612;
                next10HCF = 10 * 3.918;
                remainingHCF = (totalHCF - 25) * 2.2763;
            }

            double waterUsageCharge = first15HCF + next10HCF + remainingHCF;
            double sewerCharge = waterUsageCharge * 0.252;
            double stormCharge = waterUsageCharge * 0.0025;
            double totalCharges = waterUsageCharge + sewerCharge + stormCharge;
            double countyTaxes = totalCharges * 0.005;
            double stateTaxes = totalCharges * 0.0152;
            double amountDue = totalCharges + countyTaxes + stateTaxes;

            txtTotalHCF.Text = totalHCF.ToString("F");
            txtNext10HCF.Text = next10HCF.ToString("F");
            txtAmountDue.Text = amountDue.ToString("F");
            txtStateTaxes.Text = stateTaxes.ToString("F");
            txtFirst15HCF.Text = first15HCF.ToString("F");
            txtSewerCharges.Text = sewerCharge.ToString("F");
            txtStormCharges.Text = stormCharge.ToString("F");
            txtLocalTaxes.Text = countyTaxes.ToString("F");
            txtTotalGallons.Text = totalGallons.ToString("F");
            txtRemainingHCF.Text = remainingHCF.ToString("F");
            txtTotalCharges.Text = totalCharges.ToString("F");
            txtLatePaymentAmountDue.Text = (amountDue + 8.95).ToString("F");
            txtWaterUsageCharges.Text = waterUsageCharge.ToString("F");
        }

        private void btnUpdateWaterBill_Click(object sender, EventArgs e)
        {
            if (string.IsNullOrEmpty(txtBillNumber.Text))
            {
                MessageBox.Show("You must enter the bill number of the water " +
                                "bill you want to update (and click the Open button).",
                                "Water Distribution Company");
                return;
            }

            if (string.IsNullOrEmpty(txtAccountNumber.Text))
                return;

            if (string.IsNullOrEmpty(txtMeterNumber.Text))
                return;

            XmlNode xnOriginalWaterBill = null;

            XmlDocument xdWaterBills = new XmlDocument();
            FileInfo fiWaterBills = new FileInfo("../../WaterBills.xml");

            if (fiWaterBills.Exists == true)
            {
                using (FileStream fsWaterBills = new FileStream(fiWaterBills.FullName, FileMode.Open,
                                                                FileAccess.Read, FileShare.Read))
                {
                    xdWaterBills.Load(fsWaterBills);

                    XmlNodeList xnlWaterBills = xdWaterBills.DocumentElement.ChildNodes;

                    foreach (XmlNode xnWaterBill in xnlWaterBills)
                    {
                        foreach (XmlNode xnBillNumber in xnWaterBill.ChildNodes)
                        {
                            if (xnBillNumber.InnerText == txtBillNumber.Text)
                            {
                                xnOriginalWaterBill = xnWaterBill;
                                break;
                            }
                        }
                    }
                }
            }

            XmlElement xeUpdatedWaterBill = xdWaterBills.CreateElement("water-bill");

            string strUpdatedWaterBill = "<bill-number>" + txtBillNumber.Text + "</bill-number>" +
                                         "<account-number>" + txtAccountNumber.Text + "</account-number>" +
                                         "<meter-reading-start-date>" + dtpServiceStartDate.Value.ToShortDateString() + "</meter-reading-start-date>" +
                                         "<meter-reading-end-date>" + dtpServiceEndDate.Value.ToShortDateString() + "</meter-reading-end-date>" +
                                         "<number-of-days>" + txtNumberOfDays.Text + "</number-of-days>" +
                                         "<counter-reading-start>" + txtCounterReadingStart.Text + "</counter-reading-start>" +
                                         "<counter-reading-end>" + txtCounterReadingEnd.Text + "</counter-reading-end>" +
                                         "<total-hcf>" + txtTotalHCF.Text + "</total-hcf>" +
                                         "<total-gallons>" + txtTotalGallons.Text + "</total-gallons>" +
                                         "<first-15-hcf>" + txtFirst15HCF.Text + "</first-15-hcf>" +
                                         "<next-10-hcf>" + txtNext10HCF.Text + "</next-10-hcf>" +
                                         "<remaining-hcf>" + txtRemainingHCF.Text + "</remaining-hcf>" +
                                         "<sewer-charges>" + txtSewerCharges.Text + "</sewer-charges>" +
                                         "<storm-charges>" + txtStormCharges.Text + "</storm-charges>" +
                                         "<water-usage-charges>" + txtWaterUsageCharges.Text + "</water-usage-charges>" +
                                         "<total-charges>" + txtTotalCharges.Text + "</total-charges>" +
                                         "<local-taxes>" + txtLocalTaxes.Text + "</local-taxes>" +
                                         "<state-taxes>" + txtStateTaxes.Text + "</state-taxes>" +
                                         "<payment-due-date>" + txtPaymentDueDate.Text + "</payment-due-date>" +
                                         "<amount-due>" + txtAmountDue.Text + "</amount-due>" +
                                         "<late-payment-due-date>" + txtLatePaymentDueDate.Text + "</late-payment-due-date>" +
                                         "<late-amount-due>" + txtLatePaymentAmountDue.Text + "</late-amount-due>";

            xeUpdatedWaterBill.InnerXml = strUpdatedWaterBill;

            xdWaterBills.DocumentElement.ReplaceChild(xeUpdatedWaterBill, xnOriginalWaterBill);

            using (FileStream fsCustomers = new FileStream(fiWaterBills.FullName, FileMode.OpenOrCreate, FileAccess.ReadWrite, FileShare.ReadWrite))
            {
                xdWaterBills.Save(fsCustomers);
            }

            Close();
        }

        private void btnNewWaterBill_Click(object sender, EventArgs e)
        {
            BillPreparation bp = new BillPreparation();
            bp.ShowDialog();
        }

        private void btnClose_Click(object sender, EventArgs e)
        {
            Close();
        }
    }
}

In the Solution Explorer, right-click Form1.cs and click Rename
Type WaterDistributionCompany (to get WaterDistributionCompany.cs) and press Enter three times to display the form

Design the form as follows:

Water Distribution Company

Control	(Name)	Text
Button	btnCustomers	Customers...
Button	btnWaterMeters	Water Meters...
Button	btnNewGasBill	New Water Bill...
Button	btnWaterBillReview	Water Bill Review...
Button	btnClose	Close

On the form, double-click the Customers... button
Return to the form and double-click the Water Meters... button
Return to the form and double-click the New Water Bill... button
Return to the form and double-click the Water Bill Review... button
Return to the form and double-click the Close button

Change the document as follows:

using System;
using System.Windows.Forms;

namespace WaterDistributionCompany1
{
    public partial class WaterDistributionCompany : Form
    {
        public WaterDistributionCompany()
        {
            InitializeComponent();
        }

        private void btnCustomers_Click_1(object sender, EventArgs e)
        {
            Customers clients = new Customers();

            clients.ShowDialog();
        }

        private void btnWaterMeters_Click(object sender, EventArgs e)
        {
            WaterMeters wm = new WaterMeters();

            wm.ShowDialog();
        }

        private void btnNewWaterBill_Click(object sender, EventArgs e)
        {
            BillPreparation bp = new BillPreparation();

            bp.ShowDialog();
        }

        private void btnWaterBillReview_Click(object sender, EventArgs e)
        {
            BillEditor be = new BillEditor();
            be.ShowDialog();
        }

        private void btnClose_Click(object sender, EventArgs e)
        {
            Close();
        }
    }
}

To execute the project, on the main menu, click Debug -> Start Without Debugging:
Click the Water Meters button:
Close the Water Meters form
Click the Customers button:
Click the New Customer button:

Type the values in the text boxes as in the following table. After each record, click the Save button:

Account #	Meter #	First Name	Last Name	Address	City	County	State	ZIP Code
2958-314-5294	392-44-572	Nicholas	Thorn	2599 Phenicia Road	Silver Spring	Montgomery	MD	20906
8046-728-5060	304-861	Augustino	Derbez	7507 Westchester Ave	Washington		DC	20008
4024-850-0482	820-418	Marianne	Pattersen	10572 Maya Blvd	Frederick	Frederick	MD	20111
1848-205-3313	925-935	Frank	Nounkeu	13931 Wellington Street	College Park	Pringe George	MD	20740
7029-371-8594	293-740	Danielle	Dormand	2515 Guthierez Street	Falls Church		VA	22046

Close the Customers form
Click the green arrow to position the new bottle somwhere around the back side of the table:

Type the following values in the text boxes and select others from date time pickers:

Water Bill #	294758
Account #	7518-302-6895
Service Start Date	10/5/2020
Service End Date	1/12/2021
Meter Reading Start	163
Reading End	196

Click the Save Water Bill button
Click the New Water Bill button again

Set some values as follows:

Water Bill #	Account #	Service Start Date:	Service End Date	Counter Reading Start	Counter Reading End
682048	4820-375-2842	10/22/2020	1/18/2021	109992	109998
137579	2038-413-9680	10/22/2020	1/22/2021	137926	137975
480465	9279-570-8394	11/14/2020	2/7/2021	6268	6275
829736	7518-302-6895	1/12/2021	4/8/2021	114	118

Close the forms and return to your programming environment
Close the form and return to your programming environment

Practical Learning: Ending the Lesson

Start Microsoft Visual Studio and create a Windows Forms application named GasUtilityCompany1
On the main menu, click Project -> Add New Item...
In the left list of the Add New Item dialog box, click Data. In the middle list, click XML File
Change the file name to GasMeters
Click Add

Change the content of the document as follows:

<?xml version="1.0" encoding="utf-8" ?>
<?xml version="1.0" encoding="utf-8" ?>
<gas-meters>
	<gas-meter>
		<meter-number>582741-38</meter-number>
		<make>Sinton International</make>
		<model>D-244</model>
		<meter-reading-date>2021-05-10</meter-reading-date>
		<counter-value>138</counter-value>
	</gas-meter>
	<gas-meter>
		<meter-number>293847-27</meter-number>
		<make>Archimeda</make>
		<model>LP2066</model>
		<meter-reading-date>2021-08-03</meter-reading-date>
		<counter-value>2866</counter-value>
	</gas-meter>
	<gas-meter>
		<meter-number>928731-59</meter-number>
		<make>EnvioSmart</make>
		<model>84-D9703</model>
		<meter-reading-date>2020-12-08</meter-reading-date>
		<counter-value>8016</counter-value>
	</gas-meter>
	<gas-meter>
		<meter-number>520246-85</meter-number>
		<make>Garland Worldwide</make>
		<model>GFH-2260</model>
		<meter-reading-date>2021-05-21</meter-reading-date>
		<counter-value>22683</counter-value>
	</gas-meter>
	<gas-meter>
		<meter-number>797047-27</meter-number>
		<make>Archimeda</make>
		<model>LP2066</model>
		<meter-reading-date>2021-10-04</meter-reading-date>
		<counter-value>725</counter-value>
	</gas-meter>
	<gas-meter>
		<meter-number>425837-14</meter-number>
		<make>EnvioSmart</make>
		<model>28-G4428</model>
		<meter-reading-date>2021-01-01</meter-reading-date>
		<counter-value>6114</counter-value>
	</gas-meter>
	<gas-meter>
		<meter-number>162460-82</meter-number>
		<make>Archimeda</make>
		<model>Di8000</model>
		<meter-reading-date>2020-06-03</meter-reading-date>
		<counter-value>15502</counter-value>
	</gas-meter>
	<gas-meter>
		<meter-number>864085-92</meter-number>
		<make>Sinton International</make>
		<model>D-244</model>
		<meter-reading-date>2021-10-05</meter-reading-date>
		<counter-value>83</counter-value>
	</gas-meter>
</gas-meters>

On the main menu of Microsoft Visual Studio, click Project -> Add Form (Windows Forms)...
Change the file name to GasMeters as the name of the form
Click Add

Design the form as follows:

Control	(Name)	Text	Other Properties
ListView	lvwWaterMeters		FullRowSelect: True GridLines: True Anchor: Top, Bottom, Left, Right
Button	btnClose	Close	Anchor: Bottom, Right

List View Columns

(Name)	Text	TextAlign	Width
colNumber	#		20
colMeterNumber	Meter Number	Center	80
colMake	Make		110
colModel	Model		80
colMeterReadingDate	Reading Date	Center	80
colCounterValue	Counter Value	Right	80

Double-click an unoccupied area of the form to launch its Load event
Return to the form and double-click the Close button

Change the document as follows:

using System;
using System.IO;
using System.Xml;
using System.Windows.Forms;

namespace QuatroGasCompany1
{
    public partial class GasMeters : Form
    {
        public GasMeters()
        {
            InitializeComponent();
        }

        private void GasMeters_Load(object sender, EventArgs e)
        {
            // Indicate the name of the file that holds the gas meters records
            string fnGasMeters = "../../GasMeters.xml";
            // Create an XML DOM
            XmlDocument xdGasMeters = new XmlDocument();

            // Check that a file for gas meters was already created
            if (File.Exists(fnGasMeters))
            {
                // If that file exists already, open it and store its records in the XML DOM
                xdGasMeters.Load(fnGasMeters);
                // Get the root of the XML DOM
                XmlElement xeGasMeter = xdGasMeters.DocumentElement;
                // Get a list of the elements under the root of the DOM
                XmlNodeList xnlGasMeters = xeGasMeter.ChildNodes;

                // This small natural number will be used to count the number of gas meters
                int i = 0;

                // Just in case the list view was displaying some records, remove them
                lvwGasMeters.Items.Clear();

                // Visit each XML document in the document
                foreach (XmlNode xnGasMeter in xnlGasMeters)
                {
                    // Create a list view item that will hold each record in the list view.
                    // Get the record counter in the first column 
                    ListViewItem lviGasMeter = new ListViewItem((i + 1).ToString()); // #

                    /* Get each part of the gas meter to display in its respective column. 
                     * Put it value in the list held by the list view item. */
                    lviGasMeter.SubItems.Add(xnGasMeter.FirstChild.InnerText); // Meter #
                    lviGasMeter.SubItems.Add(xnGasMeter.FirstChild.NextSibling.InnerText); // Make
                    lviGasMeter.SubItems.Add(xnGasMeter.FirstChild.NextSibling.NextSibling.InnerText); // Model
                    lviGasMeter.SubItems.Add(xnGasMeter.FirstChild.NextSibling.NextSibling.NextSibling.InnerText); // Meter Reading Date
                    lviGasMeter.SubItems.Add(xnGasMeter.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.InnerText); // Counter Value
                    // Add the list view item to the list view
                    lvwGasMeters.Items.Add(lviGasMeter);

                    // Increase the counter of records
                    i++;
                }
            }
        }

        private void btnClose_Click(object sender, EventArgs e)
        {
            Close();
        }
    }
}

To create a new form, on the main menu, click Project -> Add Form (Windows Forms)...
Change the file Name to CustomerNew
Click Add

Using the Properties window, change the following characteristics of the form:

FormBorderStyle: FixedDialog
Text:            Gas Utility Company - New Customer
StartPosition:   CenterScreen
MaximizeBox:	   False
MinimizeBox:	   False

Design the form as follows:

Control	(Name)	Text	Other Properies
Label		Account #:
TextBox	txtAccountNumber		Modifiers: Internal
Label		Meter #:
TextBox	txtMeterNumber		Modifiers: Internal
Label		Meter Details:
TextBox	txtMeterDetails		Modifiers: Internal
Label		First Name:
TextBox	txtFirstName		Modifiers: Internal
Label		Last Name:
TextBox	txtLastName		Modifiers: Internal
Label		Address:
TextBox	txtAddress		Modifiers: Internal
Label		City:
TextBox	txtCity		Modifiers: Internal
Label		County:
TextBox	txtCounty		Modifiers: Internal
Label		State:
TextBox	txtState		Modifiers: Internal
Label		ZIP Code:
TextBox	txtZIPCode
Button	btnSave	Save Customer Account	DialogResult: OK
Button	btnClose	Close	DialogResult: Cancel

Click the form to select it and, using the Properties window, change the following characteristics:
```
AcceptButton: btnSave
CancelButton: btnClose
```
To create a new form, on the main menu, click Project -> Add Form (Windows Forms)...
Change the file name to CustomerEditor
Click Add

Using the Properties window, change the following characteristics of the form:

FormBorderStyle: FixedDialog
Text:            Gas Utility Company - Customer Editor
StartPosition:   CenterScreen
MaximizeBox:	   False
MinimizeBox:	   False

Design the form as follows:

Control	(Name)	Text	Other Properties
Label		Account #:
TextBox	txtAccountNumber		Modifiers: Internal
Button	btnOpen	Open
Label		Meter #:
TextBox	txtMeterNumber		Modifiers: Internal
Label		Meter Details:
TextBox	txtMeterDetails		Modifiers: Internal
Label		First Name:
TextBox		txtFirstName	Modifiers: Internal
Label		Last Name:
TextBox	txtLastName		Modifiers: Internal
Label		Address:
TextBox	txtAddress		Modifiers: Internal
Label		City:
TextBox	txtCity		Modifiers: Internal
Label		County:
TextBox	txtCounty		Modifiers: Internal
Label		State:
TextBox	txtState		Modifiers: Internal
Label		ZIP Code:
TextBox	txtZIPCode		Modifiers: Internal
Button	btnUpdateGasMeter	Update Gas Meter	DialogResult: OK
Button	btnClose	Close	DialogResult: Cancel

Click the form to select it and, using the Properties window, change the following characteristics:
```
AcceptButton: btnUpdateGasMeter
CancelButton: btnClose
```
On the form, click the Meter # text box
In the Properties window, click the Events button
Double-click Leave
Return to the form and double-click the Open button

Change the document as follows:

using System;
using System.IO;
using System.Xml;
using System.Windows.Forms;

namespace QuatroGasCompany1
{
    public partial class CustomerEditor : Form
    {
        public CustomerEditor()
        {
            InitializeComponent();
        }

        public void IdentifyGasMeter()
        {
            if (string.IsNullOrEmpty(txtMeterNumber.Text))
                return;

            XmlDocument xdGasMeters = new XmlDocument();
            FileInfo fiGasMeters = new FileInfo("../../GasMeters.xml");

            /* This code will run if the user had first put a valid account number; then this 
             * code is used to find the water meter associated with the customer's account. */
            if(fiGasMeters.Exists == true )
            {
                // Open the file that contains the water meter details
                using (FileStream fsGasMeters = new FileStream(fiGasMeters.FullName, FileMode.Open,
                                                               FileAccess.Read, FileShare.Read))
                {
                    // Store the list of water meters in an XML DOM
                    xdGasMeters.Load(fiGasMeters.FullName);

                    // Create a list of elements based on a node named meter-number
                    XmlNodeList xnlGasMeters = xdGasMeters.DocumentElement.GetElementsByTagName("meter-number");

                    // Visit each node of the list of elements
                    foreach (XmlNode xnGasMeter in xnlGasMeters)
                    {
                        // If you find a meter number that is the same as the meter number from the form, ...
                        if (xnGasMeter.InnerText == txtMeterNumber.Text)
                        {
                            // ... display its details
                            txtMeterDetails.Text = xnGasMeter.NextSibling.InnerText + " " + xnGasMeter.NextSibling.NextSibling.InnerText + " (Meter #: " + txtMeterNumber.Text + ")";
                        }
                    }
                }
            }
        }

        private void txtMeterNumber_Leave(object sender, EventArgs e)
        {
            XmlDocument xdCustomers = new XmlDocument();
            string strCustomers = "../../Customers.xml";
            FileInfo fiCustomers = new FileInfo(strCustomers);

            if (fiCustomers.Exists == true)
            {
                using (FileStream fsCustomers = new FileStream(fiCustomers.FullName, FileMode.Open,
                                                               FileAccess.Read, FileShare.Read))
                {
                    xdCustomers.Load(fsCustomers);

                    XmlNodeList xnlCustomers = xdCustomers.DocumentElement.GetElementsByTagName("account-number");

                    foreach (XmlNode xnCustomer in xnlCustomers)
                    {
                        if (xnCustomer.InnerText == txtAccountNumber.Text)
                        {
                            txtMeterNumber.Text = xnCustomer.NextSibling.InnerText;
                            txtFirstName.Text = xnCustomer.NextSibling.NextSibling.InnerText;
                            txtLastName.Text = xnCustomer.NextSibling.NextSibling.NextSibling.InnerText;
                            txtAddress.Text = xnCustomer.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                            txtCity.Text = xnCustomer.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                            txtCounty.Text = xnCustomer.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                            txtState.Text = xnCustomer.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                            txtZIPCode.Text = xnCustomer.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;

                            break;
                        }
                    }
                }
            }

            IdentifyGasMeter();
        }

        private void btnOpen_Click(object sender, EventArgs e)
        {
            string strCustomers = "../../Customers.xml";
            XmlDocument xdCustomers = new XmlDocument();
            FileInfo fiCustomers = new FileInfo(strCustomers);

            if( File.Exists(fiCustomers.FullName) == true )
            {
                using (FileStream fsCustomers = new FileStream(fiCustomers.FullName, FileMode.Open,
                                                               FileAccess.Read, FileShare.Read))
                {
                    xdCustomers.Load(fsCustomers);

                    XmlNodeList xnlCustomers = xdCustomers.DocumentElement.GetElementsByTagName("account-number");

                    foreach (XmlNode xnCustomer in xnlCustomers)
                    {
                        if (xnCustomer.InnerText == txtAccountNumber.Text)
                        {
                            txtMeterNumber.Text = xnCustomer.NextSibling.InnerText;
                            txtFirstName.Text = xnCustomer.NextSibling.NextSibling.InnerText;
                            txtLastName.Text = xnCustomer.NextSibling.NextSibling.NextSibling.InnerText;
                            txtAddress.Text = xnCustomer.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                            txtCity.Text = xnCustomer.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                            txtCounty.Text = xnCustomer.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                            txtState.Text = xnCustomer.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                            txtZIPCode.Text = xnCustomer.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;

                            break;
                        }
                    }
                }
            }

            IdentifyGasMeter();
        }
    }
}

To create another form, on the main menu, click Project -> Add New Form (Windows Forms)...
Change the file name to Customers
Click Add

Using the Properties window, change the following characteristics of the form:

Text:          Gas Utility Company - Customers
StartPosition: CenterScreen
MaximizeBox:	 False

Design the form as follows:

Control	(Name)	Text	Other Properties
ListView	lvwCustomers		FullRowSelect: True GridLines: True Anchor: Top, Bottom, Left, Right
Button	btnNewCustomer	New Customer	Anchor: Bottom, Right
Button	btnCustomerEditor	Customer Editor...	Anchor: Bottom, Right
Button	btnClose	Close	Anchor: Bottom, Right

List View Columns

(Name)	Text	TextAlign	Width
colNumber	#		20
colAccountNumber	Account #		90
colMeterNumber	Meter Number	Center	80
colFirstName	First Name		65
colLastName	Last Name		65
colAddress	Address		135
colCity	City		80
colCounty	County		80
colState	State	Center	40
colZIPCode	ZIP Code

Double-click an unoccupied area of the form to generate its Load event
Return to the form and double-click the New Customer button
Return to the form and double-click the Customer Editor button
Return to the form and double-click the Close button

Change the document as follows:

using System;
using System.IO;
using System.Xml;
using System.Windows.Forms;

namespace QuatroGasCompany1
{
    public partial class Customers : Form
    {
        public Customers()
        {
            InitializeComponent();
        }

        void ShowCustomers()
        {
            XmlDocument xdCustomers = new XmlDocument();
            FileInfo fiCustomers = new FileInfo("../../Customers.xml");

            if (fiCustomers.Exists)
            {
                xdCustomers.Load(fiCustomers.FullName);
                XmlElement xeCustomer = xdCustomers.DocumentElement;
                XmlNodeList xnlCustomers = xeCustomer.ChildNodes;

                int i = 1;

                lvwCustomers.Items.Clear();

                foreach (XmlNode xnCustomer in xnlCustomers)
                {
                    ListViewItem lviCustomer = new ListViewItem(i.ToString()); // #

                    lviCustomer.SubItems.Add(xnCustomer.FirstChild.InnerText); // Account #
                    lviCustomer.SubItems.Add(xnCustomer.FirstChild.NextSibling.InnerText); // Meter #
                    lviCustomer.SubItems.Add(xnCustomer.FirstChild.NextSibling.NextSibling.InnerText); // First Name
                    lviCustomer.SubItems.Add(xnCustomer.FirstChild.NextSibling.NextSibling.NextSibling.InnerText); // Last Name
                    lviCustomer.SubItems.Add(xnCustomer.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.InnerText); // Address
                    lviCustomer.SubItems.Add(xnCustomer.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText); // City
                    lviCustomer.SubItems.Add(xnCustomer.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText); // County
                    lviCustomer.SubItems.Add(xnCustomer.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText); // State
                    lviCustomer.SubItems.Add(xnCustomer.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText); // ZIP Code

                    lvwCustomers.Items.Add(lviCustomer);

                    i++;
                }
            }
        }

        private void Customers_Load(object sender, EventArgs e)
        {
            ShowCustomers();
        }

        private void btnNewCustomer_Click(object sender, EventArgs e)
        {
            CustomerNew cn = new CustomerNew();

            if (cn.ShowDialog() == DialogResult.OK)
            {
                if (string.IsNullOrEmpty(cn.txtAccountNumber.Text))
                {
                    MessageBox.Show("You must enter a (unique) account number for the customer." +
                                    Environment.NewLine +
                                    "We cannot create a customer account that doesn't have an account number.",
                                    "Gas Utility Company");

                    // If the user doesn't provide an account number, don't do nothing.
                    return;
                }

                if (string.IsNullOrEmpty(cn.txtMeterNumber.Text))
                {
                    MessageBox.Show("You must type a (unique) number for the gas meter.", "Gas Utility Company");

                    // If the user doesn't provide a meter number, don't do nothing.
                    return;
                }

                XmlDocument xdCustumers = new XmlDocument();
                FileInfo fiCustomers = new FileInfo("../../Customers.xml");

                if (fiCustomers.Exists == true)
                {
                    using (FileStream fsCustumers = new FileStream(fiCustomers.FullName, FileMode.Open,
                                                                   FileAccess.Read, FileShare.Read))
                    {
                        xdCustumers.Load(fsCustumers);
                    }
                }
                else
                {
                    xdCustumers.LoadXml("<?xml version=\"1.0\" encoding=\"utf-8\"?>" +
                                        "<custumers></custumers>");
                }

                XmlElement xeCustumer = xdCustumers.CreateElement("custumer");
                string strCustumer    = "<account-number>" + cn.txtAccountNumber.Text + "</account-number>" +
                                        "<meter-number>" + cn.txtMeterNumber.Text + "</meter-number>" +
                                        "<first-name>" + cn.txtFirstName.Text + "</first-name>" +
                                        "<last-name>" + cn.txtLastName.Text + "</last-name>" +
                                        "<address>" + cn.txtAddress.Text + "</address>" +
                                        "<city>" + cn.txtCity.Text + "</city>" +
                                        "<county>" + cn.txtCounty.Text + "</county>" +
                                        "<state>" + cn.txtState.Text + "</state>" +
                                        "<zip-code>" + cn.txtZIPCode.Text + "</zip-code>";

                xeCustumer.InnerXml = strCustumer;
                xdCustumers.DocumentElement.PrependChild(xeCustumer);

                using (FileStream fsCustumers = new FileStream(fiCustomers.FullName, FileMode.OpenOrCreate,
                                                               FileAccess.Write, FileShare.Write))
                {
                    xdCustumers.Save(fsCustumers);
                }
            }

            ShowCustomers();
        }

        private void btnCustomerEditor_Click(object sender, EventArgs e)
        {
            CustomerEditor ce = new CustomerEditor();

            if( ce.ShowDialog() == DialogResult.OK)
            {
                if (string.IsNullOrEmpty(ce.txtAccountNumber.Text))
                    return;

                if (string.IsNullOrEmpty(ce.txtMeterNumber.Text))
                    return;

                XmlNode xnExisting = null;

                XmlDocument xdCustomers = new XmlDocument();
                string strCustomers = "../../Customers.xml";
                FileInfo fiCustomers = new FileInfo(strCustomers);

                if (fiCustomers.Exists == true)
                {
                    using (FileStream fsCustomers = new FileStream(fiCustomers.FullName, FileMode.Open,
                                                                   FileAccess.Read, FileShare.Read))
                    {
                        xdCustomers.Load(fsCustomers);

                        XmlNodeList xnlCustomers = xdCustomers.DocumentElement.ChildNodes;

                        foreach (XmlNode xnCustomer in xnlCustomers)
                        {
                            foreach (XmlNode xnAccountNumber in xnCustomer.ChildNodes)
                            {
                                if (xnAccountNumber.InnerText == ce.txtAccountNumber.Text)
                                {
                                    xnExisting = xnCustomer;
                                    break;
                                }
                            }
                        }
                    }
                }

                XmlElement xeUpdatedCustomer = xdCustomers.CreateElement("customer");

                string strUpdatedCustomer = "<account-number>" + ce.txtAccountNumber.Text + "</account-number>" +
                                            "<meter-number>" + ce.txtMeterNumber.Text + "</meter-number>" +
                                            "<first-name>" + ce.txtFirstName.Text + "</first-name>" +
                                            "<last-name>" + ce.txtLastName.Text + "</last-name>" +
                                            "<address>" + ce.txtAddress.Text + "</address>" +
                                            "<city>" + ce.txtCity.Text + "</city>" +
                                            "<county>" + ce.txtCounty.Text + "</county>" +
                                            "<state>" + ce.txtState.Text + "</state>" +
                                            "<zip-code>" + ce.txtZIPCode.Text + "</zip-code>";

                xeUpdatedCustomer.InnerXml = strUpdatedCustomer;

                xdCustomers.DocumentElement.ReplaceChild(xeUpdatedCustomer, xnExisting);

                using (FileStream fsCustomers = new FileStream(fiCustomers.FullName, FileMode.OpenOrCreate,
                                                               FileAccess.ReadWrite, FileShare.ReadWrite))
                {
                    xdCustomers.Save(fsCustomers);
                }
            }

            ShowCustomers();
        }

        private void btnClose_Click(object sender, EventArgs e)
        {
            Close();
        }
    }
}

To create a new form, on the Solution Explorer, right-click WaterDistributionCompany -> Add -> Form (Windows Forms)...
Change the file Name to BillPreparation
Click Add
To create a new form, on the main menu, click Project -> Add Form (Windows Forms)...
Change the file name to BillEditor
Click Add
Click the BillPreparation.cs [Design] tab to return to the Bill Preparation form

Design the form as follows:

Control	(Name)	Text	Other Properties
Label		Customer Account Information	Font: Microsoft Sans Serif, 9.75pt, style=Bold
Label		Account #:
TextBox	txtAccountNumber
Label		Customer Name:
TextBox	txtCustomerName
TextBox	txtAddress
TextBox	txtCity
TextBox:	txtCounty
TextBox	txtState
TextBox	txtZIPCode
Label		Meter Information	Font: Microsoft Sans Serif, 9.75pt, style=Bold
Label		Meter Details:
TextBox	txtMeterNumber
TextBox	txtMeterDetails
Label		Meter Reading
Label		___________________
Label		Reading Start Date:
Label		Reading End Date:
MonthCalendar	mcReadingStartDate
MonthCalendar	mcReadingEndDate
Label		Counter Readiing Start:
TextBox	txtCounterReadiingStart		TextAlign: Right
Label		Counter Readiing End:
TextBox	txtCounterReadiingEnd		TextAlign: Right
Label		Number of Days:
TextBox	txtNumberOfDays		TextAlign: Right
Label		Total CCF:
TextBox	txtTotalHCF		TextAlign: Right
Label		Total Therms (CCF * 1.0367):
TextBox	txtTotalTherms		TextAlign: Right
Label		Bill Values	Font: Microsoft Sans Serif, 9.75pt, style=Bold
Label		Transportation Charges:
TextBox	txtTransportationCharges		TextAlign: Right
Label		Delivery Total:
TextBox	txtDeliveryTotal		TextAlign: Right
Label		Distrib. Adjust (*0.13086):
TextBox	txtDistributionAdjustment		TextAlign: Right
Label		Environmental Charges:
TextBox	txtEnvironmentalCharges		TextAlign: Right
Label		First 50 Therms (* 0.5269):
TextBox	txtFirst50Therms		TextAlign: Right
Label		Over 50 Therms (* 0.4995):
TextBox	txtOver50Therms		TextAlign: Right
Label	Local/County Taxes:
TextBox	txtLocalTaxes		RightAlign: Right
Label		State Taxes:
TextBox	txtStateTaxes
Label		Total Charges:
TextBox	txtTotalCharges		RightAlign: Right
Label		_________________________
Label		Payment Due Date:
TextBox	txtPaymentDueDate		TextAlign: Right
Label		Amount Due:
TextBox	txtAmountDue		TextAlign: Right
Label		Late Payment Due Date:
TextBox	txtLatePaymentDueDate		TextAlign: Right
Label		Late Payment Amount Due:
TextBox	txtLatePaymentAmountDue		TextAlign: Right
Label		____________________________
Label		Bill #:
TextBox	txtBillNumber		TextAlign: Right
Button	btnSaveGasBill	Save Gas Bill
Button	btnReviewGasBill	Review Gas Bill...
Button	btnClose	Close

Double-click an unoccupied area of the form to access its Load event
Return to the form and click the Account # text box
In the Properties window, click the Events button
In the Events section of the Properties window, double-click Leave
Return to the form and double-click the Reading Start Date month calendar
Return to the form and double-click the Reading End Date month calendar
Return to the form and click the Counter Reading End text box
In the Events section of the Properties window, double-click Leave
Return to the form and double-click the Save Gas Bill button
Return to the form and double-click the Review Gas Bill button
Return to the form and double-click the Close button

Change the document as follows:

using System;
using System.IO;
using System.Xml;
using System.Windows.Forms;

namespace QuatroGasCompany1
{
    public partial class BillPreparation : Form
    {
        public BillPreparation()
        {
            InitializeComponent();
        }

        private void BillPreparation_Load(object sender, EventArgs e)
        {
            Random rndBillNumber = new Random();

            txtBillNumber.Text = rndBillNumber.Next(100001, 999999).ToString();
        }

        private void txtAccountNumber_Leave(object sender, EventArgs e)
        {
            if (string.IsNullOrEmpty(txtAccountNumber.Text))
                return;

            string fnCustumers = "../../Customers.xml";
            XmlDocument xdCustumers = new XmlDocument();
            FileInfo fiCustumers = new FileInfo(fnCustumers);

            if (fiCustumers.Exists == true)
            {
                xdCustumers.Load(fnCustumers);
                XmlElement xeCustumer = xdCustumers.DocumentElement;
                XmlNodeList xnlCustumers = xeCustumer.ChildNodes;

                foreach (XmlNode xnCustumer in xnlCustumers)
                {
                    foreach (XmlNode xnAccount in xnCustumer.ChildNodes)
                    {
                        if (xnAccount.InnerText == txtAccountNumber.Text)
                        {
                            txtMeterNumber.Text = xnAccount.NextSibling.InnerText;
                            txtCustomerName.Text = xnAccount.NextSibling.NextSibling.InnerText + " " +
                                                   xnAccount.NextSibling.NextSibling.NextSibling.InnerText;
                            txtAddress.Text = xnAccount.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                            txtCity.Text = xnAccount.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                            txtCounty.Text = xnAccount.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                            txtState.Text = xnAccount.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                            txtZIPCode.Text = xnAccount.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                        }
                    }
                }
            }

            string fnGasMeters = "../../GasMeters.xml";
            XmlDocument xdGasMeters = new XmlDocument();

            if (string.IsNullOrEmpty(txtMeterNumber.Text))
                return;

            if (File.Exists(fnGasMeters))
            {
                xdGasMeters.Load(fnGasMeters);
                XmlElement xeGasMeter = xdGasMeters.DocumentElement;
                XmlNodeList xnlGasMeters = xeGasMeter.ChildNodes;

                foreach (XmlNode xnGasMeter in xnlGasMeters)
                {
                    if (xnGasMeter.FirstChild.InnerText == txtMeterNumber.Text)
                    {
                        txtMeterDetails.Text = xnGasMeter.FirstChild.NextSibling.InnerText + " " + xnGasMeter.FirstChild.NextSibling.NextSibling.InnerText;
                        mcReadingStartDate.SelectionStart = DateTime.Parse(xnGasMeter.FirstChild.NextSibling.NextSibling.NextSibling.InnerText);
                        txtCounterReadingStart.Text = xnGasMeter.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                    }
                }
            }
        }

        private void mcReadingStartDate_DateChanged(object sender, DateRangeEventArgs e)
        {
            DateTime dtStart = mcReadingStartDate.SelectionStart;
            DateTime dtEnd = mcReadingEndDate.SelectionStart;
            TimeSpan tsDays = dtEnd.Subtract(dtStart);

            txtNumberOfDays.Text = tsDays.Days.ToString();

            txtPaymentDueDate.Text = mcReadingEndDate.SelectionStart.AddDays(21).ToShortDateString();
            txtLatePaymentDueDate.Text = mcReadingEndDate.SelectionStart.AddMonths(1).ToShortDateString();
        }

        private void mcReadingEndDate_DateChanged(object sender, DateRangeEventArgs e)
        {
            mcReadingStartDate_DateChanged(sender, e);
        }

        private void txtCounterReadingEnd_Leave(object sender, EventArgs e)
        {
            if (string.IsNullOrEmpty(txtAccountNumber.Text))
            {
                MessageBox.Show("You must enter the starting value of the counter reading.",
                                "Quatro Gas Company");
                return;
            }

            if (string.IsNullOrEmpty(txtMeterNumber.Text))
            {
                MessageBox.Show("You must enter the meter number of the gas meter used by " +
                                "the customer (normally, this is done by entering the customer's account number).",
                                "Quatro Gas Company");
                return;
            }

            if (string.IsNullOrEmpty(txtCounterReadingEnd.Text))
            {
                MessageBox.Show("You must enter the ending value of the counter reading.",
                                "Quatro Gas Company");
                return;
            }

            int meterReadingStart = int.Parse(txtCounterReadingStart.Text);
            int meterReadingEnd = int.Parse(txtCounterReadingEnd.Text);

            int consumption = meterReadingEnd - meterReadingStart;

            double totalTherms = consumption * 1.0367;
            double first50Therms, over50Therms;

            if (totalTherms < 50)
            {
                first50Therms = totalTherms * 0.5269;
                over50Therms = 0;
            }
            else
            {
                first50Therms = 50 * 0.5269;
                over50Therms = (totalTherms - 50) * 0.4995;
            }

            /* We will use some random values for the transportation charge (my 
             * research didn't make it clear to me how gas companies set this price. */
            Random rndTransportation = new Random();
            double[] transportationValues = { 9.75, 9.95, 10.25, 10.45, 10.85, 12.55, 13.50, 14.35 };

            double transportationCharges = transportationValues[rndTransportation.Next(1, transportationValues.Length)];
            double deliveryTotal = transportationCharges + first50Therms + over50Therms;

            double distribution = totalTherms * 0.11086;
            double environment = deliveryTotal * 0.0045;
            double state = transportationCharges * 0.0225;
            double local = transportationCharges * 0.05826;
            double totalCharges = transportationCharges + deliveryTotal + distribution + environment + local + state;
            double amtDue = totalCharges;

            txtStateTaxes.Text = state.ToString("F");
            txtLocalTaxes.Text = local.ToString("F");
            txtAmountDue.Text = amtDue.ToString("F");
            txtCCFTotal.Text = consumption.ToString();
            txtTotalTherms.Text = totalTherms.ToString("F");
            txtOver50Therms.Text = over50Therms.ToString("F");
            txtTotalCharges.Text = totalCharges.ToString("F");
            txtFirst50Therms.Text = first50Therms.ToString("F");
            txtDeliveryTotal.Text = deliveryTotal.ToString("F");
            txtEnvironmentalCharges.Text = environment.ToString("F");
            txtDistributionAdjustment.Text = distribution.ToString("F");
            txtLatePaymentAmountDue.Text = (amtDue + 8.35).ToString("F");
            txtTransportationCharges.Text = transportationCharges.ToString("F");
        }

        private void btnSaveGasBill_Click(object sender, EventArgs e)
        {
            if (string.IsNullOrEmpty(txtAccountNumber.Text))
            {
                MessageBox.Show("You must enter a (unique) account number for the customer." +
                                Environment.NewLine +
                                "We cannot create a customer account that doesn't have an account number.",
                                "Gas Utility Company");

                return;
            }

            if (string.IsNullOrEmpty(txtMeterNumber.Text))
            {
                MessageBox.Show("You must type a (unique) number for the gas meter.", "Gas Utility Company");

                return;
            }

            if (string.IsNullOrEmpty(txtCounterReadingEnd.Text))
            {
                MessageBox.Show("You must type a the last number entered on the gas meter.", "Gas Utility Company");

                return;
            }

            string strGasBills = "../../GasBills.xml";
            XmlDocument xdGasBills = new XmlDocument();
            FileInfo fiGasBills = new FileInfo(strGasBills);

            if (File.Exists(strGasBills))
            {
                using (FileStream fsGasBills = new FileStream(fiGasBills.FullName, FileMode.Open,
                                                              FileAccess.Read, FileShare.Read))
                {
                    xdGasBills.Load(fsGasBills);
                }
            }
            else
            {
                xdGasBills.LoadXml("<?xml version=\"1.0\" encoding=\"utf-8\"?>" +
                                   "<gas-bills></gas-bills>");
            }

            XmlElement xeGasBill = xdGasBills.CreateElement("gas-bill");
            string strGasBill    = "<bill-number>" + txtBillNumber.Text + "</bill-number>" +
                                   "<account-number>" + txtAccountNumber.Text + "</account-number>" +
                                   "<reading-start-date>" + mcReadingStartDate.SelectionStart.ToShortDateString() + "</reading-start-date>" +
                                   "<reading-end-date>" + mcReadingEndDate.SelectionStart.ToShortDateString() + "</reading-end-date>" +
                                   "<counter-reading-start>" + txtCounterReadingStart.Text + "</counter-reading-start>" +
                                   "<counter-reading-end>" + txtCounterReadingEnd.Text + "</counter-reading-end>" +
                                   "<number-of-days>" + txtNumberOfDays.Text + "</number-of-days>" +
                                   "<ccf-total>" + txtCCFTotal.Text + "</ccf-total>" +
                                   "<total-therms>" + txtTotalTherms.Text + "</total-therms>" +
                                   "<transportation-charges>" + txtTransportationCharges.Text + "</transportation-charges>" +
                                   "<delivery-total>" + txtDeliveryTotal.Text + "</delivery-total>" +
                                   "<distribution-adjustment>" + txtDistributionAdjustment.Text + "</distribution-adjustment>" +
                                   "<environmental-charges>" + txtEnvironmentalCharges.Text + "</environmental-charges>" +
                                   "<first-50-therms>" + txtFirst50Therms.Text + "</first-50-therms>" +
                                   "<over-50-therms>" + txtOver50Therms.Text + "</over-50-therms>" +
                                   "<local-taxes>" + txtLocalTaxes.Text + "</local-taxes>" +
                                   "<state-taxes>" + txtStateTaxes.Text + "</state-taxes>" +
                                   "<total-charges>" + txtTotalCharges.Text + "</total-charges>" +
                                   "<payment-due-date>" + txtPaymentDueDate.Text + "</payment-due-date>" +
                                   "<amount-due>" + txtAmountDue.Text + "</amount-due>" +
                                   "<late-payment-due-date>" + txtLatePaymentDueDate.Text + "</late-payment-due-date>" +
                                   "<late-payment-amount-due>" + txtLatePaymentAmountDue.Text + "</late-payment-amount-due>";

            xeGasBill.InnerXml = strGasBill;
            xdGasBills.DocumentElement.PrependChild(xeGasBill);

            using (FileStream fsGasBills = new FileStream(strGasBills, FileMode.OpenOrCreate,
                                                           FileAccess.Write, FileShare.Write))
            {
                xdGasBills.Save(fsGasBills);
            }

            Close();
        }

        private void btnReviewGasBill_Click(object sender, EventArgs e)
        {
            BillEditor be = new BillEditor();

            be.ShowDialog();
        }

        private void btnClose_Click(object sender, EventArgs e)
        {
            Close();
        }
    }
}

Click the BillEditor.cs [Design] tab to access its form

Design the form as follows:

Control	(Name)	Text	Other Properties
Label		Customer Account Information	Font: Microsoft Sans Serif, 9.75pt, style=Bold
Label		Account #:
TextBox	txtAccountNumber
Label		Customer Name:
TextBox	txtCustomerName
TextBox	txtAddress
TextBox	txtCity
TextBox:	txtCounty
TextBox	txtState
TextBox	txtZIPCode
Label		Meter Information	Georgia, 9.75pt, style=Bold, Italic
Label		Meter Details:
TextBox	txtMeterNumber
TextBox	txtMeterDetails
Label		Meter Reading
Label		___________________
Label		Reading Start Date:
Label		Reading End Date:
MonthCalendar	mcReadingStartDate
MonthCalendar	mcReadingEndDate
Label		Counter Readiing Start:
TextBox	txtCounterReadiingStart		TextAlign: Right
Label		Counter Readiing End:
TextBox	txtCounterReadiingEnd		TextAlign: Right
Label		Number of Days:
TextBox	txtNumberOfDays		TextAlign: Right
Label		Total CCF:
TextBox	txtTotalHCF		TextAlign: Right
Label		Total Therms (CCF * 1.0367):
TextBox	txtTotalTherms		TextAlign: Right
Label		Bill Values	Font: Microsoft Sans Serif, 9.75pt, style=Bold
Label		Transportation Charges:
TextBox	txtTransportationCharges		TextAlign: Right
Label		Delivery Total:
TextBox	txtDeliveryTotal		TextAlign: Right
Label		Distrib. Adjust (*0.13086):
TextBox	txtDistributionAdjustment		TextAlign: Right
Label		Environmental Charges:
TextBox	txtEnvironmentalCharges		TextAlign: Right
Label		First 50 Therms (* 0.5269):
TextBox	txtFirst50Therms		TextAlign: Right
Label		Over 50 Therms (* 0.4995):
TextBox	txtOver50Therms		TextAlign: Right
Label		Local/County Taxes:
TextBox	txtLocalTaxes		RightAlign: Right
Label		State Taxes:
TextBox	txtStateTaxes
Label		Total Charges:
TextBox	txtTotalCharges		RightAlign: Right
Label		_________________________
Label		Payment Due Date:
TextBox	txtPaymentDueDate		TextAlign: Right
Label		Amount Due:
TextBox	txtAmountDue		TextAlign: Right
Label		Late Payment Due Date:
TextBox	txtLatePaymentDueDate		TextAlign: Right
Label		Late Payment Amount Due:
TextBox	txtLatePaymentAmountDue		TextAlign: Right
Label		____________________________
Label		Bill #:
TextBox	txtBillNumber		TextAlign: Right
Button	btnOpenGasBill	Open Gas Bill
Button	btnSaveGasBill	Save Gas Bill
Button	btnClose	Close

On the form, double-click the Open button
Return to the form and double-click the Save Gaser Bill button
Return to the form and double-click the Review Gas Bill button
Return to the form and double-click the Close button

Change the document as follows:

using System;
using System.IO;
using System.Xml;
using System.Windows.Forms;

namespace QuatroGasCompany1
{
    public partial class BillEditor : Form
    {
        public BillEditor()
        {
            InitializeComponent();
        }

        void IdentifyCustomer()
        {
            if (string.IsNullOrEmpty(txtAccountNumber.Text))
                return;

            string fnCustumers = "../../Customers.xml";
            XmlDocument xdCustumers = new XmlDocument();
            FileInfo fiCustumers = new FileInfo(fnCustumers);

            if (fiCustumers.Exists == true)
            {
                xdCustumers.Load(fnCustumers);
                XmlElement xeCustumer = xdCustumers.DocumentElement;
                XmlNodeList xnlCustumers = xeCustumer.ChildNodes;

                foreach (XmlNode xnCustumer in xnlCustumers)
                {
                    foreach (XmlNode xnAccount in xnCustumer.ChildNodes)
                    {
                        if (xnAccount.InnerText == txtAccountNumber.Text)
                        {
                            txtMeterNumber.Text = xnAccount.NextSibling.InnerText;
                            txtCustomerName.Text = xnAccount.NextSibling.NextSibling.InnerText + " " +
                                                   xnAccount.NextSibling.NextSibling.NextSibling.InnerText;
                            txtAddress.Text = xnAccount.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                            txtCity.Text = xnAccount.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                            txtCounty.Text = xnAccount.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                            txtState.Text = xnAccount.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                            txtZIPCode.Text = xnAccount.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;

                            break;
                        }
                    }
                }
            }

            string fnGasMeters = "../../GasMeters.xml";
            XmlDocument xdGasMeters = new XmlDocument();

            if (string.IsNullOrEmpty(txtMeterNumber.Text))
                return;

            if (File.Exists(fnGasMeters))
            {
                xdGasMeters.Load(fnGasMeters);
                XmlElement xeGasMeter = xdGasMeters.DocumentElement;
                XmlNodeList xnlGasMeters = xeGasMeter.ChildNodes;

                foreach (XmlNode xnGasMeter in xnlGasMeters)
                {
                    if (xnGasMeter.FirstChild.InnerText == txtMeterNumber.Text)
                    {
                        txtMeterDetails.Text = xnGasMeter.FirstChild.NextSibling.InnerText + " " + xnGasMeter.FirstChild.NextSibling.NextSibling.InnerText;
                        mcReadingStartDate.SelectionStart = DateTime.Parse(xnGasMeter.FirstChild.NextSibling.NextSibling.NextSibling.InnerText);
                        txtCounterReadingStart.Text = xnGasMeter.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;

                        break;
                    }
                }
            }
        }

        private void btnOpenGasBill_Click(object sender, EventArgs e)
        {
            string strGasBills = "../../GasBills.xml";
            XmlDocument xdGasBills = new XmlDocument();
            FileInfo fiGasBills = new FileInfo(strGasBills);

            if (File.Exists(strGasBills))
            {
                using (FileStream fsGasBills = new FileStream(fiGasBills.FullName, FileMode.Open,
                                                              FileAccess.Read, FileShare.Read))
                {
                    xdGasBills.Load(fsGasBills);
                    XmlNodeList xnlGasBills = xdGasBills.DocumentElement.ChildNodes;

                    foreach (XmlNode xnGasBill in xnlGasBills)
                    {
                        if (xnGasBill.FirstChild.InnerText == txtBillNumber.Text)
                        {
                            txtAccountNumber.Text             =                xnGasBill.FirstChild.NextSibling.InnerText;// strAccountNumber;
                            mcReadingStartDate.SelectionStart = DateTime.Parse(xnGasBill.FirstChild.NextSibling.NextSibling.InnerText);
                            mcReadingEndDate.SelectionStart   = DateTime.Parse(xnGasBill.FirstChild.NextSibling.NextSibling.NextSibling.InnerText);
                            txtCounterReadingStart.Text       =                xnGasBill.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                            txtCounterReadingEnd.Text         =                xnGasBill.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                            txtNumberOfDays.Text              =                xnGasBill.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                            txtCCFTotal.Text                  =                xnGasBill.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                            txtTotalTherms.Text               =                xnGasBill.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                            txtTransportationCharges.Text     =                xnGasBill.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                            txtDeliveryTotal.Text             =                xnGasBill.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                            txtDistributionAdjustment.Text    =                xnGasBill.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                            txtEnvironmentalCharges.Text      =                xnGasBill.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                            txtFirst50Therms.Text             =                xnGasBill.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                            txtOver50Therms.Text              =                xnGasBill.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                            txtLocalTaxes.Text                =                xnGasBill.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                            txtStateTaxes.Text                =                xnGasBill.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                            txtTotalCharges.Text              =                xnGasBill.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                            txtPaymentDueDate.Text            =                xnGasBill.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                            txtAmountDue.Text                 =                xnGasBill.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                            txtLatePaymentDueDate.Text        =                xnGasBill.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;
                            txtLatePaymentAmountDue.Text      =                xnGasBill.FirstChild.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.NextSibling.InnerText;

                            // break;
                        }
                    }
                }
            }

            IdentifyCustomer();
        }

        private void btnSaveGasBill_Click(object sender, EventArgs e)
        {
            if( string.IsNullOrEmpty(txtBillNumber.Text))   
                return;
            
            if (string.IsNullOrEmpty(txtAccountNumber.Text))    
                return;
            
            XmlNode xnOriginalBill = null;
            
            XmlDocument xdGasBills = new XmlDocument();
            string strGasBills = "../../GasBills.xml";
            FileInfo fiGasBills = new FileInfo(strGasBills);
            
            if (fiGasBills.Exists == true)    
            {
                using (FileStream fsGasBills = new FileStream(fiGasBills.FullName, FileMode.Open,
                                                              FileAccess.Read, FileShare.Read))    
                {
                    xdGasBills.Load(fsGasBills);
                    
                    XmlNodeList xnlGasBills = xdGasBills.DocumentElement.ChildNodes;
                    
                    foreach (XmlNode xnGasBill in xnlGasBills)    
                    {
                        foreach (XmlNode xnBillNumber in xnGasBill.ChildNodes)    
                        {
                            if(xnBillNumber.InnerText == txtBillNumber.Text)    
                            {
                                xnOriginalBill = xnGasBill;
                                break;    
                            }
                        }
                    }
                }
            }
            
            XmlElement xeReviewedGasBill = xdGasBills.CreateElement("gas-bill");
            
            string strGasBill = "<bill-number>" + txtBillNumber.Text + "</bill-number>" +
                                "<account-number>" + txtAccountNumber.Text + "</account-number>" +
                                "<reading-start-date>" + mcReadingStartDate.SelectionStart.ToShortDateString() + "</reading-start-date>" +
                                "<reading-end-date>" + mcReadingEndDate.SelectionStart.ToShortDateString() + "</reading-end-date>" +
                                "<counter-reading-start>" + txtCounterReadingStart.Text + "</counter-reading-start>" +
                                "<counter-reading-end>" + txtCounterReadingEnd.Text + "</counter-reading-end>" +
                                "<number-of-days>" + txtNumberOfDays.Text + "</number-of-days>" +
                                "<ccf-total>" + txtCCFTotal.Text + "</ccf-total>" +
                                "<total-therms>" + txtTotalTherms.Text + "</total-therms>" +
                                "<transportation-charges>" + txtTransportationCharges.Text + "</transportation-charges>" +
                                "<delivery-total>" + txtDeliveryTotal.Text + "</delivery-total>" +
                                "<distribution-adjustment>" + txtDistributionAdjustment.Text + "</distribution-adjustment>" +
                                "<environmental-charges>" + txtEnvironmentalCharges.Text + "</environmental-charges>" +
                                "<first-50-therms>" + txtFirst50Therms.Text + "</first-50-therms>" +
                                "<over-50-therms>" + txtOver50Therms.Text + "</over-50-therms>" +
                                "<local-taxes>" + txtLocalTaxes.Text + "</local-taxes>" +
                                "<state-taxes>" + txtStateTaxes.Text + "</state-taxes>" +
                                "<total-charges>" + txtTotalCharges.Text + "</total-charges>" +
                                "<payment-due-date>" + txtPaymentDueDate.Text + "</payment-due-date>" +
                                "<amount-due>" + txtAmountDue.Text + "</amount-due>" +
                                "<late-payment-due-date>" + txtLatePaymentDueDate.Text + "</late-payment-due-date>" +
                                "<late-payment-amount-due>" + txtLatePaymentAmountDue.Text + "</late-payment-amount-due>";

            xeReviewedGasBill.InnerXml = strGasBill;

            xdGasBills.DocumentElement.ReplaceChild(xeReviewedGasBill, xnOriginalBill);
            
            using (FileStream fsCustomers = new FileStream(fiGasBills.FullName, FileMode.OpenOrCreate,
                                                           FileAccess.ReadWrite, FileShare.ReadWrite))    
            {
                xdGasBills.Save(fsCustomers);
                
            }

            btnClose_Click(sender, e);
        }

        private void btnClose_Click(object sender, EventArgs e)
        {
            Close();
        }
    }
}

In the Solution Explorer, right-click Form1.cs and click Rename
Type GasDistribution (to get WaterDistributionCompany.cs) and press Enter three times to display the form

Design the form as follows:

Water Distribution Company

Control	(Name)	Text
Button	btnCustomers	Customers...
Button	btnGasMeters	Gas Meters...
Button	btnNewGasBill	New Gas Bill...
Button	btnGasBillReview	Gas Bill Review...
Button	btnClose	Close

On the form, double-click the Customers... button
Return to the form and double-click the Gas Meters... button
Return to the form and double-click the New Gas Bill... button
Return to the form and double-click the Gas Bill Review... button
Return to the form and double-click the Close button

Change the document as follows:

using System;
using System.Windows.Forms;

namespace QuatroGasCompany1
{
    public partial class GasDistribution : Form
    {
        public GasDistribution()
        {
            InitializeComponent();
        }

        private void btnCustomers_Click(object sender, EventArgs e)
        {
            Customers clients = new Customers();

            clients.ShowDialog();
        }

        private void btnWaterMeters_Click(object sender, EventArgs e)
        {
            GasMeters wm = new GasMeters();

            wm.ShowDialog();
        }

        private void btnNewGasBill_Click(object sender, EventArgs e)
        {
            BillPreparation bp = new BillPreparation();
            bp.ShowDialog();
        }

        private void btnGasBillReview_Click(object sender, EventArgs e)
        {
            BillEditor be = new BillEditor();
            be.ShowDialog();
        }

        private void btnClose_Click(object sender, EventArgs e)
        {
            Close();
        }
    }
}

To execute the project, on the main menu, click Debug -> Start Without Debugging:
Click the Water Meters button:
Close the Water Meters form
Click the Customers button:
Click the New Customer button:

Type the values in the text boxes as in the following table. After each record, click the Save button:

Account #	Meter #	First Name	Last Name	Address	City	County	State	ZIP Code
2958-314-5294	392-44-572	Nicholas	Thorn	2599 Phenicia Road	Silver Spring	Montgomery	MD	20906
8046-728-5060	304-861	Augustino	Derbez	7507 Westchester Ave	Washington		DC	20008
4024-850-0482	820-418	Marianne	Pattersen	10572 Maya Blvd	Frederick	Frederick	MD	20111
1848-205-3313	925-935	Frank	Nounkeu	13931 Wellington Street	College Park	Pringe George	MD	20740
7029-371-8594	293-740	Danielle	Dormand	2515 Guthierez Street	Falls Church		VA	22046

Close the Customers form
Click the green arrow to position the new bottle somwhere around the back side of the table:

Type the following values in the text boxes and select others from date time pickers:

Water Bill #	294758
Account #	7518-302-6895
Service Start Date	10/5/2020
Service End Date	1/12/2021
Meter Reading Start	163
Reading End	196

Click the Save Water Bill button
Click the New Water Bill button again

Set some values as follows:

Water Bill #	Account #	Service Start Date:	Service End Date	Counter Reading Start	Counter Reading End
682048	4820-375-2842	10/22/2020	1/18/2021	109992	109998
137579	2038-413-9680	10/22/2020	1/22/2021	137926	137975
480465	9279-570-8394	11/14/2020	2/7/2021	6268	6275
829736	7518-302-6895	1/12/2021	4/8/2021	114	118

Close the forms and return to your programming environment
Close the form and return to your programming environment
Close your programming environment


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