using System;
using System.Drawing;
using System.Collections;
using System.ComponentModel;
using System.Windows.Forms;
using System.Xml;

namespace CPAP3a
{
		 
			. . . No Change
	

		private void btnNewMake_Click(object sender, System.EventArgs e)
		{
			NewMake frmNewMake = new NewMake();

			frmNewMake.ShowDialog();
		}
	}
}

private void NewPart_Load(object sender, System.EventArgs e)
{
	// Fill the Year combo box with years from 1960 to the coming year
	for(int i = DateTime.Now.Year+1; i >= 1960; i--)
		this.cboYears.Items.Add(i.ToString());

	// We will generate a random number for the item
	// To start, we will use the miliseconds as a seed
	DateTime tmeNow = DateTime.Now;
	int ms = tmeNow.Millisecond;

	// Now we can generate a random number between 100000 and 999999
	Random rndNumber = new Random(ms);

	// Generate three randomg characters
	Char firstCharacter  = (Char)(rndNumber.Next(65, 90));
		Char secondCharacter = (Char)(rndNumber.Next(65, 90));
	Char thirdCharacter  = (Char)(rndNumber.Next(65, 90));
	// Generate a random number made of 4 digits
	int numberPart = rndNumber.Next(1000, 9999);
	 
	// Exclude the digits 1 and 0 because they create confusion
	if( firstCharacter == 'I' || firstCharacter == 'O' )
		firstCharacter = 'A';
	if( secondCharacter == 'I' || secondCharacter == 'O' )
		secondCharacter = 'A';
	if( thirdCharacter == 'I' || thirdCharacter == 'O' )
		thirdCharacter = 'A';
	// Generate a random number between 1 and 3
	int rndCombination = rndNumber.Next(1, 4);
	string strPartNumber = null;

	// Create a part number using some algorithm
	if( rndCombination == 1 )
	strPartNumber = firstCharacter.ToString() + secondCharacter.ToString() +
			numberPart.ToString() + thirdCharacter.ToString());
	else if( rndCombination == 2 )
		strPartNumber = firstCharacter.ToString() + numberPart.ToString() +
			secondCharacter.ToString() + thirdCharacter.ToString());
	else if( rndCombination == 3 )
		strPartNumber = numberPart.ToString() + firstCharacter.ToString() +
			secondCharacter.ToString() + thirdCharacter.ToString());
	else
		strPartNumber = rndNumber.Next(100000, 999999).ToString();

	// Display the new number in the Part # text box
	this.txtPartNumber.Text = strPartNumber;

	// Disable the OK button to indicate that the part is not ready
	this.btnAddPart.Enabled = false;
}

using System;
using System.Drawing;
using System.Collections;
using System.ComponentModel;
using System.Windows.Forms;
using System.Xml;

namespace CPAP3a
{
	
	. . . No Change
		
		
private void btnNewMake_Click(object sender, System.EventArgs e)
{
	NewMake frmNewMake = new NewMake();

	frmNewMake.ShowDialog();
}

private void btnNewModel_Click(object sender, System.EventArgs e)
{
	NewModel frmNewModel = new NewModel();

	 frmNewModel.ShowDialog();
}

private void btnNewCategory_Click(object sender, System.EventArgs e)
{
	NewPartCategory frmCat = new NewPartCategory();

	 frmCat.ShowDialog();
}

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

private void OrderProcessing_Load(object sender, System.EventArgs e)
{
// Fill the Year combo box with years from 1960 to the coming year
	for(int i = DateTime.Now.Year+1; i >= 1960; i--)
		this.cboYears.Items.Add(i.ToString());
}

using System;
using System.Drawing;
using System.Collections;
using System.ComponentModel;
using System.Windows.Forms;
using System.IO;
using System.Xml;

private void btnNewPart_Click(object sender, System.EventArgs e)
{
	NewPart frmPart = new NewPart();

	frmPart.ShowDialog();
}

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

private void btnOrderProcessing_Click(object sender, System.EventArgs e)
{
	OrderProcessing frmOrder = new OrderProcessing();

	frmOrder.ShowDialog();
}

private void btnNewPart_Click(object sender, System.EventArgs e)
{
	NewPart frmPart = new NewPart();

	frmPart.ShowDialog();
}

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

private void NewModel_Load(object sender, System.EventArgs e)
{
	// We will need a reference to the XML document
	XmlDocument docXML = new XmlDocument();

	// We will start with the Make combo box
	// Open the Cars.xml file
	docXML.Load("Cars.xml");
	// Get a reference to the root node
	XmlElement nodRoot = docXML.DocumentElement;
	// Locate all nodes whose name is Make
	XmlNodeList nodItems = nodRoot.GetElementsByTagName("Make");
	// Retrieve the value of each Make node and put 
	// that value in the Make combo box
	for(int i = 0; i < nodItems.Count; i++)
		this.cboMakes.Items.Add(nodItems[i].Attributes["MakeName"].InnerText);
}

private void NewPart_Load(object sender, System.EventArgs e)
{
	// Fill the Year combo box with years from 1960 to the coming year
	for(int i = DateTime.Now.Year+1; i >= 1960; i--)
		this.cboYears.Items.Add(i.ToString());

	// We will need a reference to the XML document
	XmlDocument docXML = new XmlDocument();

	// Open the Cars.xml file
	docXML.Load("Cars.xml");

	// Get a reference to the root node
	XmlElement nodRoot = docXML.DocumentElement;
	// Locate all nodes whose name is Make
	XmlNodeList nodItems = nodRoot.GetElementsByTagName("Make");
	// Retrieve the value of each Make node and put 
	// that value in the Make combo box
	for(int i = 0; i < nodItems.Count; i++)
		this.cboMakes.Items.Add(nodItems[i].Attributes["MakeName"].InnerText);

	// Open the Makes.xml file
	docXML.Load("PartCategories.xml");

	// Get a reference to the root node
	nodRoot = docXML.DocumentElement;
	// Locate all nodes whose name is Make
	nodItems = nodRoot.GetElementsByTagName("PartCategory");
	// Retrieve the value of each Make node and put 
	// that value in the Make combo box
	for(int i = 0; i < nodItems.Count; i++)
		this.cboPartCategories.Items.Add(nodItems[i].InnerText);

	this.cboPartCategories.Text = "Miscellaneous";

	// We will generate a random number for the item
	// To start, we will use the miliseconds as a seed
	DateTime tmeNow = DateTime.Now;
	int ms = tmeNow.Millisecond;

	// Now we can generate a random number between 100000 and 999999
	Random rndNumber = new Random(ms);

	// Generate three randomg characters
	Char firstCharacter  = (Char)(rndNumber.Next(65, 90));
	Char secondCharacter = (Char)(rndNumber.Next(65, 90));
	Char thirdCharacter  = (Char)(rndNumber.Next(65, 90));
	// Generate a random number made of 4 digits
	int numberPart = rndNumber.Next(1000, 9999);
	 
	// Exclude the digits 1 and 0 because they create confusion
	if( firstCharacter == 'I' || firstCharacter == 'O' )
		firstCharacter = 'A';
	if( secondCharacter == 'I' || secondCharacter == 'O' )
		secondCharacter = 'A';
	if( thirdCharacter == 'I' || thirdCharacter == 'O' )
		thirdCharacter = 'A';
	// Generate a random number between 1 and 3
	int rndCombination = rndNumber.Next(1, 4);
	string strPartNumber = null;

	// Create a part number using some algorithm
	if( rndCombination == 1 )
		strPartNumber = firstCharacter.ToString() + secondCharacter.ToString() +
			numberPart.ToString() + thirdCharacter.ToString();
	else if( rndCombination == 2 )
		strPartNumber = firstCharacter.ToString() + numberPart.ToString() +
			secondCharacter.ToString() + thirdCharacter.ToString();
	else if( rndCombination == 3 )
		strPartNumber = numberPart.ToString() + firstCharacter.ToString() +
			secondCharacter.ToString() + thirdCharacter.ToString();
	else
		strPartNumber = rndNumber.Next(100000, 999999).ToString();

	// Display the new number in the Part # text box
	this.txtPartNumber.Text = strPartNumber;

	// Disable the OK button to indicate that the part is not ready
	this.btnAddPart.Enabled = false;
}

<?xml version="1.0" encoding="utf-8" ?> 
<Cars>
	<!-- Each car model is organized as follows:
	       1. The first part identifies the make of the car.
	           We use a MakeName attribute of the Make element
	           to identify a make
	       2. The second part identifies the name of the model.
	-->
	<Make MakeName="Acura">
		<Model>Integra GS 1.8L L4</Model>
		<Model>MDX 3.5L V6</Model>
		<Model>NSX 3.0L V6</Model>
		<Model>NSX 3.2L V6</Model>
		<Model>TL 3.2L V6</Model>
	</Make>
	<Make MakeName="Audi">
		<Model>A4 Quattro 1.8L Turbo</Model>
		<Model>A4 Quattro 3.0L V6</Model>
		<Model>S4 2.7L V6</Model>
	</Make>
	<Make MakeName="BMW">
		<Model>325I 2.5L L6</Model>
		<Model>325XI 2.5L L6</Model>
		<Model>745I 4.4L V8</Model>
		<Model>Z3 Coupe 3.0L L6</Model>
	</Make>
</Cars>

private void btnNewMake_Click(object sender, System.EventArgs e)
{
	// The new car make will come from the New Make dialog box
	 NewMake frmMake = new NewMake();

	 // Display the New Make dialog box and find out if the user clicked OK
	 if( frmMake.ShowDialog() == DialogResult.OK )
	 {
		 string strNewMake = frmMake.txtNewMake.Text;

		 // If the user didn't create a new Make, don't do anything
		 if( strNewMake == "" )
			 return;

		 // Before adding the new make, check that it doesn't exist already
		 if( this.cboMakes.FindStringExact(strNewMake) > 0 )
			 return;

		 // Now you can add it
		 this.cboMakes.Items.Add(strNewMake);
		 // The user likely wants this new item selected
		 this.cboMakes.Text = strNewMake;

		 // Open the Cars.xml file
		 XmlDocument docXMLFile = new XmlDocument();
		 docXMLFile.Load("Cars.xml");

		 // Get the root node so we can explore its children
		 XmlNode nodRoot = docXMLFile.DocumentElement;
		 
		 // If the car is not in the list already, create its Make node
		 XmlNode nodNewMake  = docXMLFile.CreateNode(XmlNodeType.Element, "Make", "");
		 // Create an attribute for the node
		 ((XmlElement)(nodNewMake)).SetAttribute("MakeName", strNewMake);
		 
		 // Add the new node to the XML file
		 docXMLFile.DocumentElement.AppendChild(nodNewMake);
		 
		 // Save the file
		 docXMLFile.Save("Cars.xml");
	}
}

private void btnNewMake_Click(object sender, System.EventArgs e)
{
	// The new car make will come from the New Make dialog box
	 NewMake frmMake = new NewMake();

	 // Display the New Make dialog box and find out if the user clicked OK
	 if( frmMake.ShowDialog() == DialogResult.OK )
	 {
		 string strNewMake = frmMake.txtNewMake.Text;

		 // If the user didn't create a new Make, don't do anything
		 if( strNewMake == "" )
			 return;

		 // Before adding the new make, check that it doesn't exist already
		 if( this.cboMakes.FindStringExact(strNewMake) > 0 )
			 return;

		 // Now you can add it
		 this.cboMakes.Items.Add(strNewMake);
		 // The user likely wants this new item selected
		 this.cboMakes.Text = strNewMake;

		 // Open the Cars.xml file
		 XmlDocument docXMLFile = new XmlDocument();
		 docXMLFile.Load("Cars.xml");

		 // Get the root node so we can explore its children
		 XmlNode nodRoot = docXMLFile.DocumentElement;
		 
		 // If the car is not in the list already, create its Make node
		 XmlNode nodNewMake  = docXMLFile.CreateNode(XmlNodeType.Element, "Make", "");
		 // Create an attribute for the node
		 ((XmlElement)(nodNewMake)).SetAttribute("MakeName", strNewMake);
		 
		 // Add the new node to the XML file
		 docXMLFile.DocumentElement.AppendChild(nodNewMake);
		 
		 // Save the file
		 docXMLFile.Save("Cars.xml");
	}
}

private void btnNewModel_Click(object sender, System.EventArgs e)
{
	// The new car model will come from the New Model dialog box
	 NewModel frmModel = new NewModel();

	 // Display the New Model dialog box and find out if the user clicked OK
	 if( frmModel.ShowDialog() == DialogResult.OK )
	 {
		 // Retrieve the values that the user specified
		 string strMake     = frmModel.cboMakes.Text;
		 string strNewModel = frmModel.txtNewModel.Text;

		 // If the new didn't select a Make, don't do anything
		 if( strMake.Equals("") )
			 return;
		 // If the New Model string is empty, don't do anything
		 if( strNewModel.Equals("") )
			 return;

		 // Open the Cars.xml file
		 XmlDocument docXMLFile = new XmlDocument();
		 docXMLFile.Load("Cars.xml");

		 // Get the root node so we can explore its children
		 XmlNode nodRoot = docXMLFile.DocumentElement;
		 
		 // Create a list of all Make nodes
		 XmlNodeList lstMakes = docXMLFile.GetElementsByTagName("Make");

		 // Visit each Make
		 for(int i = 0; i < lstMakes.Count; i++)
		 {
			 // Get a reference to the current node
			 XmlNode curMake = lstMakes[i];

			 // If, or when you find the Make
			 if( curMake.Attributes["MakeName"].InnerText.Equals(strMake) )
			 {
				 // Since we found the Make, find out if the model exists
				 XmlNodeList lstCurrentModels = curMake.ChildNodes;

				 // Check each model if the list already contains the model
				 for(int j = 0; j < lstCurrentModels.Count; j++)
				 {
				if( lstCurrentModels[j].InnerText.Equals(strNewModel) )
					 {
			MessageBox.Show("That model exists already in the database");
						 return;
					 }
				 }

				 // create a child node to it
	    XmlNode nodModel = docXMLFile.CreateNode(XmlNodeType.Element, "Model", "");
			 // Create its value using the string from the New Make dialog box
				 nodModel.InnerText = strNewModel;
				 // Add the new element at the end of the file
				 curMake.AppendChild(nodModel);

				 // Save the file
				 docXMLFile.Save("Cars.xml");
				 break;
			 }
		 }
	}
}

private void cboMakes_SelectedIndexChanged(object sender, System.EventArgs e)
{
	// Empty the Models combo box
	this.cboModels.Items.Clear();

	// Find out if the user had selected a Make
	string strSelectedMake = this.cboMakes.Text;
	// Open the Cars.xml file
	XmlDocument docXML = new XmlDocument();
	docXML.Load("Cars.xml");

	// Get a reference to the root node
	XmlElement nodRoot = docXML.DocumentElement;
	// Locate all nodes whose name is Make
	XmlNodeList nodMakes = nodRoot.GetElementsByTagName("Make");
	// Look for the Make that is the same the user selected
	for(int i = 0; i < nodMakes.Count; i++)
	{
		// Retrieve the value of each Make node and put
	string strMakeName = nodMakes[i].Attributes["MakeName"].InnerText;
		// If you find it...
		if( strMakeName.Equals(strSelectedMake) )
		{
			// If you find it, make a list of its models...
		XmlNodeList nodAvailableModels = nodMakes[i].ChildNodes;
		// ... then add each of its models to the Model combo box
			for(int j = 0; j < nodAvailableModels.Count; j++)
		this.cboModels.Items.Add(nodAvailableModels[j].InnerText);
		}
	}
}

private void btnNewCategory_Click(object sender, System.EventArgs e)
{
	// Get a reference to the New Part Category form
	 NewPartCategory frmCategory = new NewPartCategory();

	 // Display the New Part Category dialog box and find out if the user clicked OK
	 if( frmCategory.ShowDialog() == DialogResult.OK )
	 {
		 string strCategory = frmCategory.txtNewCategory.Text;

		 // If the user didn't create a new category, don't do anything
		 if( strCategory.Equals("") )
			 return;

		 // Before adding the new category, check that it doesn't exist already
		 if( this.cboPartCategories.FindStringExact(strCategory) > 0 )
			 return;

		 // Now you can add it
		 this.cboPartCategories.Items.Add(strCategory);
		 // The user likely wants this new item selected
		 this.cboPartCategories.Text = strCategory;

		 // Open the PartCategories.xml file
		 XmlDocument docXMLFile = new XmlDocument();
		 docXMLFile.Load("PartCategories.xml");

		 // Get the root node so we can explore its children
		 XmlNode nodRoot = docXMLFile.DocumentElement;
		 
		 // If the new part is not in the list already, create its node
XmlNode nodNewCategory  = docXMLFile.CreateNode(XmlNodeType.Element, "PartCategory", "");
		 // Create text for the node
		 nodNewCategory.InnerText = strCategory;
		 
		 // Add the new node to the XML file
		 docXMLFile.DocumentElement.AppendChild(nodNewCategory);
		 
		 // Save the file
		 docXMLFile.Save("PartCategories.xml");
	}
}

private void txtPartName_TextChanged(object sender, System.EventArgs e)
{
	// If there is no part name, no need to add the item to the XML file
	if( this.txtPartName.Text == "" )
		this.btnAddPart.Enabled = false;
	else
		this.btnAddPart.Enabled = true;
}

private void txtUnitPrice_TextChanged(object sender, System.EventArgs e)
{
	// If the price is not specified, don't add the item to the XML file
	if( this.txtUnitPrice.Text == "" )
		this.btnAddPart.Enabled = false;
	else
		this.btnAddPart.Enabled = true;
}

private void txtPartNumber_TextChanged(object sender, System.EventArgs e)
{
	// Make sure that there is a Part Number for this item
	// Otherwise, don't add the part to the XML file
	if( this.txtPartNumber.Text == "" )
		this.btnAddPart.Enabled = false;
	else
		this.btnAddPart.Enabled = true;
}

private void btnAddPart_Click(object sender, System.EventArgs e)
{
	// Open the Parts.xml file
	XmlDocument docXML = new XmlDocument();
	docXML.Load("Parts.xml");

	// Before adding the new part, make sure all components are ready
	// Otherwise, don't add it
	if( this.cboYears.SelectedIndex < 0 )
	{
		MessageBox.Show("You must specify the year. " +
			"This will help to locate the part");
		this.cboYears.Focus();
		return;
	}
	if( this.cboMakes.SelectedIndex < 0 )
	{
		MessageBox.Show("Please select the car make for this part.");
		this.cboMakes.Focus();
		return;
	}
	if( this.cboModels.SelectedIndex < 0 )
	{
		MessageBox.Show("The car model is required. " +
			"It helps to know the specific car this part is made for.");
		this.cboModels.Focus();
		return;
	}
	if( this.txtPartName.Text.Equals("") )
	{
	MessageBox.Show("You must specify the part name or a (very) short description.");
		this.txtPartName.Focus();
		return;
	}
	if( this.txtUnitPrice.Text.Equals("") )
	{
		MessageBox.Show("You must enter the price of each unit of this part.");
		this.txtUnitPrice.Focus();
		return;
	}
	if( this.txtPartNumber.Text.Equals("") )
	{
		MessageBox.Show("Every item of this database must have a number. " +
			"The number is just a combination of letters and digits." +
			"Please make up a number and enter it in the Part # box.");
		this.txtPartNumber.Focus();
		return;
	}

	// The part seems to be ready
	// Get a reference to the root node
	XmlElement nodNewPart = docXML.CreateElement("Part");
	// Create a new part as a child of the root (this is a simple node addition
	string strNewPart = "<PartNumber>", this.txtPartNumber.Text, "</PartNumber>" +
				"<CarYear>", this.cboYears.Text, "</CarYear>" +
				"<Make>", this.cboMakes.Text, "</Make>" +
				"<Model>", this.cboModels.Text, "</Model>" +
				"<PartName Category=\"", this.cboPartCategories.Text,"\">" +
				this.txtPartName.Text, "</PartName>" +
				"<UnitPrice>", this.txtUnitPrice.Text, "</UnitPrice>");
	nodNewPart.InnerXml = strNewPart;
	docXML.DocumentElement.AppendChild(nodNewPart);
	docXML.Save("Parts.xml");

	// Reset the form in case the user wants to add another part
	this.cboYears.SelectedIndex = -1;
	this.cboMakes.SelectedIndex = -1;
	this.cboModels.SelectedIndex = -1;
	this.cboPartCategories.Text = "Miscellaneou";
	this.txtPartName.Text = "";
	this.txtUnitPrice.Text = "";
	 
	// We will generate a random number for the item
	// To start, we will use the miliseconds as a seed
	DateTime tmeNow = DateTime.Now;
	int ms = tmeNow.Millisecond;

	// Now we can generate a random number between 100000 and 999999
	Random rndNumber = new Random(ms);

	// Generate three randomg characters
	Char firstCharacter  = (Char)(rndNumber.Next(65, 90));
	Char secondCharacter = (Char)(rndNumber.Next(65, 90));
	Char thirdCharacter  = (Char)(rndNumber.Next(65, 90));
	// Generate a random number made of 4 digits
	int numberPart = rndNumber.Next(1000, 9999);
	 
	// Exclude the digits 1 and 0 because they create confusion
	if( firstCharacter == 'I' || firstCharacter == 'O' )
		firstCharacter = 'A';
	if( secondCharacter == 'I' || secondCharacter == 'O' )
		secondCharacter = 'A';
	if( thirdCharacter == 'I' || thirdCharacter == 'O' )
		thirdCharacter = 'A';
	// Generate a random number between 1 and 3
	int rndCombination = rndNumber.Next(1, 4);
	string strPartNumber = null;

	// Create a part number using some algorithm
	if( rndCombination == 1 )
		strPartNumber = firstCharacter.ToString() + secondCharacter.ToString() +
			numberPart.ToString() + thirdCharacter.ToString();
	else if( rndCombination == 2 )
		strPartNumber = firstCharacter.ToString() + numberPart.ToString() + 
			secondCharacter.ToString() + thirdCharacter.ToString();
	else if( rndCombination == 3 )
		strPartNumber = numberPart.ToString() + firstCharacter.ToString() +
			secondCharacter.ToString() + thirdCharacter.ToString();
	else
		strPartNumber = rndNumber.Next(100000, 999999).ToString();

	// Display the new number in the Part # text box
	this.txtPartNumber.Text = strPartNumber;
	this.cboYears.Focus();
}

private void cboYears_SelectedIndexChanged(object sender, System.EventArgs e)
{
	string strYearSelected = this.cboYears.Text;
	string strMake = null;
	XmlDocument docXML = new XmlDocument();
		
	Text = strYearSelected;
	// Open the Parts.xml file
	docXML.Load("Parts.xml");
			 
	// We will empty the Make combo box to add a new list
	this.cboMakes.Items.Clear();
// We will empty the Model combo box because the car is about to be changed
	this.cboModels.Items.Clear();
	// Also empty the list of available parts
	this.lvwAvailableParts.Items.Clear();
	 
	// Create a list of the nodes whose names are CarYear
	XmlNodeList nodYears = docXML.GetElementsByTagName("CarYear");
	// Create a list of the nodes whose names are Make
	XmlNodeList nodMakes = docXML.GetElementsByTagName("Make");

	// Check every CarYear node to see if its 
	// value matches the selected year
	for(int i = 0; i < nodYears.Count; i++)
	{
		// If the CarYear of the current node is the same as the
	// selected year, add its corresponding make to the Make combo box
		if( nodYears[i].InnerXml.Equals(strYearSelected) )
		{
			strMake = nodMakes[i].InnerText;
	// Before adding the Make to the list, make sure that it doesn't
			// exist already in the combo box
			if( !this.cboMakes.Items.Contains(strMake) )
				this.cboMakes.Items.Add(strMake);
		}
	}
}

private void cboMakes_SelectedIndexChanged(object sender, System.EventArgs e)
{
	// Get the year that was selected
	string strYearSelected = this.cboYears.Text;
	// Get the make that is selected
	string strMakeSelected = this.cboMakes.Text;
	// We will need a model string
	string strModel = null;
	// We will use a reference to the XML document
	XmlDocument docXML = new XmlDocument();
			 
	// Open the Parts.xml file
	docXML.Load("Parts.xml");
			 
	// We will empty the Model combo box to add a new list
	this.cboModels.Items.Clear();
	// Also empty the list of available parts
	this.lvwAvailableParts.Items.Clear();

	// Create a list of the nodes we will need to locate
	XmlNodeList nodYears  = docXML.GetElementsByTagName("CarYear");
	XmlNodeList nodMakes  = docXML.GetElementsByTagName("Make");
	XmlNodeList nodModels = docXML.GetElementsByTagName("Model");

	// Check every CarYear node to see if its 
	// value matches the selected year
	for(int i = 0; i < nodYears.Count; i++)
	{
		// If the CarYear of the current node is the same as the
	// selected year, check its corresponding make to see whether
		// it matches the selected Make
	// If both the year and the make selected match, then add the
		// corresponding model to the Model combo box
		if( (nodYears[i].InnerXml.Equals(strYearSelected)) &&
			(nodMakes[i].InnerXml.Equals(strMakeSelected)) )
		{
			strModel = nodModels[i].InnerText;
		// Before adding the model to the Model combo box, make sure 
			// that it doesn't exist already in the list
			if( this.cboModels.Items.Contains(strModel) )
				break;
			else // If it doesn't, then add it
				this.cboModels.Items.Add(strModel);
		}
	}
}

private void cboModels_SelectedIndexChanged_1(object sender, System.EventArgs e)
{
	// Get the year that was selected
	 string strYearSelected = this.cboYears.Text;
	 // Get the make that is selected
	 string strMakeSelected = this.cboMakes.Text;
	 // We will need a model string
	 string strModelSelected = this.cboModels.Text;

	 // We will use a reference to the XML document
	 XmlDocument docXML = new XmlDocument();		 
	 // Open the Parts.xml file
	 docXML.Load("Parts.xml");	 
	 
	 // Empty the Category combo box
	 this.cboCategories.Items.Clear();
	 // Empty the list of available parts
	 this.lvwAvailableParts.Items.Clear();

	 // Create a list of the nodes we will need to locate
	 XmlNodeList nodYears     = docXML.GetElementsByTagName("CarYear");
	 XmlNodeList nodMakes     = docXML.GetElementsByTagName("Make");
	 XmlNodeList nodModels    = docXML.GetElementsByTagName("Model");
	 XmlNodeList nodPartNames = docXML.GetElementsByTagName("PartName");

	 // Check every CarYear node to see if its 
	 // value matches the selected year
	 for(int i = 0; i < nodYears.Count; i++)
	 {
		 // If the CarYear of the current node is the same as the
	// selected year, check its corresponding make and model to see whether
		 // they match the selected Make and Model
		 if( (nodYears[i].InnerXml.Equals(strYearSelected)) &&
			 (nodMakes[i].InnerXml.Equals(strMakeSelected)) &&
			 (nodModels[i].InnerXml.Equals(strModelSelected)) )
		 {
	 // If you find a part that match the year, the make and the model selected,
	 // then retrieve the (first/only) attribute of the Part Name element
		XmlAttribute nodCategory = nodPartNames[i].Attributes["Category"];
			 // Add the category to the Categories combo box
		 string strCategory = nodCategory.InnerText;
		 // Before adding the model to the Model combo box, make sure 
			 // that it doesn't exist already in the list
			 if( this.cboCategories.Items.Contains(strCategory) )
				 break;
			 else // If it doesn't, then add it
				 this.cboCategories.Items.Add(strCategory);
		 }
	 }
}

private void cboCategories_SelectedIndexChanged(object sender, System.EventArgs e)
{
	// Get the values the user has selected
	string strYearSelected = this.cboYears.Text;
	string strMakeSelected = this.cboMakes.Text;
	string strModelSelected = this.cboModels.Text;
	string strCategorySelected = this.cboCategories.Text;
			 
	// Open the Parts.xml file
	XmlDocument docXML = new XmlDocument();
	docXML.Load("Parts.xml");
			 
	// Empty the list of available parts
	this.lvwAvailableParts.Items.Clear();
		 
	// Create a list of the nodes we will need to locate
	XmlNodeList nodYears     = docXML.GetElementsByTagName("CarYear");
	XmlNodeList nodMakes     = docXML.GetElementsByTagName("Make");
	XmlNodeList nodModels    = docXML.GetElementsByTagName("Model");
	XmlNodeList nodPartNbr   = docXML.GetElementsByTagName("PartNumber");
	XmlNodeList nodPartNames = docXML.GetElementsByTagName("PartName");
	XmlNodeList nodPrices    = docXML.GetElementsByTagName("UnitPrice");

	// Check every CarYear node to see if its 
	// value matches the selected year
	for(int i = 0; i < nodYears.Count; i++)
	{
	XmlAttribute nodCategory = nodPartNames[i].Attributes["Category"];
	// Find the year, make, model, and category that match the selected
		if( (nodYears[i].InnerXml.Equals(strYearSelected)) &&
			(nodMakes[i].InnerXml.Equals(strMakeSelected)) &&
			(nodModels[i].InnerXml.Equals(strModelSelected)) &&
			(nodCategory.InnerText.Equals(strCategorySelected)) )
		{
		// Create a list view item of the part of the current model
	ListViewItem itmPart = new ListViewItem(nodPartNbr[i].InnerText, 0);
			itmPart.SubItems.Add(nodPartNames[i].InnerText);
			itmPart.SubItems.Add(nodPrices[i].InnerText);
			// And display that list to the list view control
			this.lvwAvailableParts.Items.Add(itmPart);
		}
	}
}

internal void CalculateTotalOrder()
{
	decimal subTotal1, subTotal2, subTotal3,
		subTotal4, subTotal5, subTotal6;
	decimal orderTotal;

	// Retrieve the value of each sub total
	subTotal1 = decimal.Parse(this.txtSubTotal1.Text);
	subTotal2 = decimal.Parse(this.txtSubTotal2.Text);
	subTotal3 = decimal.Parse(this.txtSubTotal3.Text);
	subTotal4 = decimal.Parse(this.txtSubTotal4.Text);
	subTotal5 = decimal.Parse(this.txtSubTotal5.Text);
	subTotal6 = decimal.Parse(this.txtSubTotal6.Text);

	// Calculate the total value of the sub totals
	orderTotal = subTotal1 + subTotal2 + subTotal3 + 
		subTotal4 + subTotal5 + subTotal6;
			
	// Display the total order in the appropriate text box
	this.txtTotalOrder.Text = orderTotal.ToString("F");
}

private void lvwAvailableParts_DoubleClick(object sender, System.EventArgs e)
{
	ListViewItem itmSelectedPart = this.lvwAvailableParts.SelectedItems[0];
			 
	// Check if the first empty row in the Order Processing section
	// and fill it up with the newly selected item
	if( this.txtPartNumber1.Text == "" )
	{
		this.txtPartNumber1.Text = itmSelectedPart.Text;
		this.txtPartName1.Text   = itmSelectedPart.SubItems[1].Text;
		this.txtUnitPrice1.Text  = itmSelectedPart.SubItems[2].Text;
		this.txtQuantity1.Text   = "1";
		this.txtSubTotal1.Text   = itmSelectedPart.SubItems[2].Text;
		this.chkKeepRemove1.Enabled = true;
		this.chkKeepRemove1.Checked = true;
		this.txtQuantity1.Focus();
	}
	else if( this.txtPartNumber2.Text == "" )
	{
		this.txtPartNumber2.Text = itmSelectedPart.Text;
		this.txtPartName2.Text   = itmSelectedPart.SubItems[1].Text;
		this.txtUnitPrice2.Text  = itmSelectedPart.SubItems[2].Text;
		this.txtQuantity2.Text   = "1";
		this.txtSubTotal2.Text   = itmSelectedPart.SubItems[2].Text;
		this.chkKeepRemove2.Enabled = true;
		this.chkKeepRemove2.Checked = true;
		this.txtQuantity2.Focus();
	}
	else if( this.txtPartNumber3.Text == "" )
	{
		this.txtPartNumber3.Text = itmSelectedPart.Text;
		this.txtPartName3.Text   = itmSelectedPart.SubItems[1].Text;
		this.txtUnitPrice3.Text  = itmSelectedPart.SubItems[2].Text;
		this.txtQuantity3.Text   = "1";
		this.txtSubTotal3.Text   = itmSelectedPart.SubItems[2].Text;
		this.chkKeepRemove3.Enabled = true;
		this.chkKeepRemove3.Checked = true;
		this.txtQuantity3.Focus();
	}
	else if( this.txtPartNumber4.Text == "" )
	{
		this.txtPartNumber4.Text = itmSelectedPart.Text;
		this.txtPartName4.Text   = itmSelectedPart.SubItems[1].Text;
		this.txtUnitPrice4.Text  = itmSelectedPart.SubItems[2].Text;
		this.txtQuantity4.Text   = "1";
		this.txtSubTotal4.Text   = itmSelectedPart.SubItems[2].Text;
		this.chkKeepRemove4.Enabled = true;
		this.chkKeepRemove4.Checked = true;
		this.txtQuantity4.Focus();
	}
	else if( this.txtPartNumber5.Text == "" )
	{
		this.txtPartNumber5.Text = itmSelectedPart.Text;
		this.txtPartName5.Text   = itmSelectedPart.SubItems[1].Text;
		this.txtUnitPrice5.Text  = itmSelectedPart.SubItems[2].Text;
		this.txtQuantity5.Text   = "1";
		this.txtSubTotal5.Text   = itmSelectedPart.SubItems[2].Text;
		this.chkKeepRemove5.Enabled = true;
		this.chkKeepRemove5.Checked = true;
		this.txtQuantity5.Focus();
	}
	else if( this.txtPartNumber6.Text == "" )
	{
		this.txtPartNumber6.Text = itmSelectedPart.Text;
		this.txtPartName6.Text   = itmSelectedPart.SubItems[1].Text;
		this.txtUnitPrice6.Text  = itmSelectedPart.SubItems[2].Text;
		this.txtQuantity6.Text   = "1";
		this.txtSubTotal6.Text   = itmSelectedPart.SubItems[2].Text;
		this.chkKeepRemove6.Enabled = true;
		this.chkKeepRemove6.Checked = true;
		this.txtQuantity6.Focus();
	}
	else
		return;

	// Calculate the current total order and update the order
	CalculateTotalOrder();
}

private void txtQuantity1_Leave(object sender, System.EventArgs e)
{
	int qty = 0;
	decimal unitPrice = 0.00M, subTotal = 0.00M;
	
	try 
	{
		// Get the quantity of the current item
		qty = int.Parse(this.txtQuantity1.Text);
	}
	catch(FormatException)
	{
MessageBox.Show("The value you provided for the quantity of the item is invalid" +
			"\nPlease try again");
	}
			
	try 
	{
		// Get the unit price of the current item
		unitPrice = decimal.Parse(this.txtUnitPrice1.Text);
	}
	catch(FormatException)
	{
		MessageBox.Show("The unit price you provided for item is invalid" +
			"\nPlease try again");
	}
	// Calculate the current sub total
	subTotal = qty * unitPrice;

	// Display the new sub total in the corresponding text box
	this.txtSubTotal1.Text = subTotal.ToString("F");
	// Update the order
	CalculateTotalOrder();
}

private void txtQuantity2_Leave(object sender, System.EventArgs e)
{
	int qty = 0;
	decimal unitPrice = 0.00M, subTotal = 0.00M;
			
	try 
	{
		qty = int.Parse(this.txtQuantity2.Text);
	}
	catch(FormatException)
	{
MessageBox.Show("The value you provided for the quantity of the item is invalid" +
			"\nPlease try again");
	}
			
	try 
	{
		unitPrice = decimal.Parse(this.txtUnitPrice2.Text);
	}
	catch(FormatException)
	{
		MessageBox.Show("The unit price you provided for item is invalid" +
			"\nPlease try again");
	}
	subTotal = qty * unitPrice;

	this.txtSubTotal2.Text = subTotal.ToString("F");
	CalculateTotalOrder();
}

private void txtQuantity3_Leave(object sender, System.EventArgs e)
{
	int qty = 0;
	decimal unitPrice = 0.00M, subTotal = 0.00M;
			
	try 
	{	
		qty = int.Parse(this.txtQuantity3.Text);
	}
	catch(FormatException)
	{
MessageBox.Show("The value you provided for the quantity of the item is invalid" +
			"\nPlease try again");
	}
			
	try 
	{
		unitPrice = decimal.Parse(this.txtUnitPrice3.Text);
	}
	catch(FormatException)
	{
		MessageBox.Show("The unit price you provided for item is invalid" +
			"\nPlease try again");
	}
	subTotal = qty * unitPrice;

	this.txtSubTotal3.Text = subTotal.ToString("F");
	CalculateTotalOrder();
}

private void txtQuantity4_Leave(object sender, System.EventArgs e)
{
	int qty = 0;
	decimal unitPrice = 0.00M, subTotal = 0.00M;
			
	try 
	{			
		qty = int.Parse(this.txtQuantity4.Text);
	}
	catch(FormatException)
	{
MessageBox.Show("The value you provided for the quantity of the item is invalid" +
			"\nPlease try again");
	}
	
	try 
	{
		unitPrice = decimal.Parse(this.txtUnitPrice4.Text);
	}
	catch(FormatException)
	{
		MessageBox.Show("The unit price you provided for item is invalid" +
			"\nPlease try again");
	}
	subTotal = qty * unitPrice;

	this.txtSubTotal4.Text = subTotal.ToString("F");
	CalculateTotalOrder();
}

private void txtQuantity5_Leave(object sender, System.EventArgs e)
{
	int qty = 0;
	decimal unitPrice = 0.00M, subTotal = 0.00M;
			
	try 
	{	
		qty = int.Parse(this.txtQuantity5.Text);
	}
	catch(FormatException)
	{
MessageBox.Show("The value you provided for the quantity of the item is invalid" +
			"\nPlease try again");
	}
	
	try 
	{
		unitPrice = decimal.Parse(this.txtUnitPrice5.Text);
	}
	catch(FormatException)
	{
		MessageBox.Show("The unit price you provided for item is invalid" +
			"\nPlease try again");
	}
	subTotal = qty * unitPrice;

	this.txtSubTotal5.Text = subTotal.ToString("F");
	CalculateTotalOrder();
}

private void txtQuantity6_Leave(object sender, System.EventArgs e)
{
	int qty = 0;
	decimal unitPrice = 0.00M, subTotal = 0.00M;
			
	try 
	{	
		qty = int.Parse(this.txtQuantity6.Text);
	}
	catch(FormatException)
	{
MessageBox.Show("The value you provided for the quantity of the item is invalid" +
				"\nPlease try again");
	}
			
	try 
	{
		unitPrice = decimal.Parse(this.txtUnitPrice6.Text);
	}
	catch(FormatException)
	{
		MessageBox.Show("The unit price you provided for item is invalid" +
			"\nPlease try again");
	}
	subTotal = qty * unitPrice;

	this.txtSubTotal6.Text = subTotal.ToString("F");
	CalculateTotalOrder();
}

private void chkKeepRemove1_CheckedChanged(object sender, System.EventArgs e)
{
	// If the check box was unchecked
	if( this.chkKeepRemove1.Checked == false ) 
	{
		// Reset the controls of the current item
		this.txtPartNumber1.Text      = "";
		this.txtPartName1.Text = "";
		this.txtUnitPrice1.Text   = "";
		this.txtQuantity1.Text    = "0";
		this.txtSubTotal1.Text    = "0.00";
		this.chkKeepRemove1.Checked     = false;
		this.chkKeepRemove1.Enabled     = false;
		// Re-calculate the total order to update it
		CalculateTotalOrder();
	}
}

private void chkKeepRemove2_CheckedChanged(object sender, System.EventArgs e)
{
	// If the check box was unchecked
	if( this.chkKeepRemove2.Checked == false ) 
	{
		// Reset the controls of the current item
		this.txtPartNumber2.Text      = "";
		this.txtPartName2.Text = "";
		this.txtUnitPrice2.Text   = "";
		this.txtQuantity2.Text    = "0";
		this.txtSubTotal2.Text    = "0.00";
		this.chkKeepRemove2.Checked     = false;
		this.chkKeepRemove2.Enabled     = false;
		// Re-calculate the total order to update it
		CalculateTotalOrder();
	}
}

private void chkKeepRemove3_CheckedChanged(object sender, System.EventArgs e)
{
	// If the check box was unchecked
	if( this.chkKeepRemove3.Checked == false ) 
	{
		// Reset the controls of the current item
		this.txtPartNumber3.Text      = "";
		this.txtPartName3.Text = "";
		this.txtUnitPrice3.Text   = "";
		this.txtQuantity3.Text    = "0";
		this.txtSubTotal3.Text    = "0.00";
		this.chkKeepRemove3.Checked     = false;
		this.chkKeepRemove3.Enabled     = false;
		// Re-calculate the total order to update it
		CalculateTotalOrder();
	}
}

private void chkKeepRemove4_CheckedChanged(object sender, System.EventArgs e)
{
	// If the check box was unchecked
	if( this.chkKeepRemove4.Checked == false ) 
	{
		// Reset the controls of the current item
		this.txtPartNumber4.Text      = "";
		this.txtPartName4.Text = "";
		this.txtUnitPrice4.Text   = "";
		this.txtQuantity4.Text    = "0";
		this.txtSubTotal4.Text    = "0.00";
		this.chkKeepRemove4.Checked     = false;
		this.chkKeepRemove4.Enabled     = false;
		// Re-calculate the total order to update it
		CalculateTotalOrder();
	}
}

private void chkKeepRemove5_CheckedChanged(object sender, System.EventArgs e)
{
	// If the check box was unchecked
	if( this.chkKeepRemove5.Checked == false ) 
	{
		// Reset the controls of the current item
		this.txtPartNumber5.Text      = "";
		this.txtPartName5.Text = "";
		this.txtUnitPrice5.Text   = "";
		this.txtQuantity5.Text    = "0";
		this.txtSubTotal5.Text    = "0.00";
		this.chkKeepRemove5.Checked     = false;
		this.chkKeepRemove5.Enabled     = false;
		// Re-calculate the total order to update it
		CalculateTotalOrder();
	}
}

private void chkKeepRemove6_CheckedChanged(object sender, System.EventArgs e)
{
	// If the check box was unchecked
	if( this.chkKeepRemove6.Checked == false ) 
	{
		// Reset the controls of the current item
		this.txtPartNumber6.Text      = "";
		this.txtPartName6.Text = "";
		this.txtUnitPrice6.Text   = "";
		this.txtQuantity6.Text    = "0";
		this.txtSubTotal6.Text    = "0.00";
		this.chkKeepRemove6.Checked     = false;
		this.chkKeepRemove6.Enabled     = false;
		// Re-calculate the total order to update it
		CalculateTotalOrder();
	}
}

private void btnSave_Click(object sender, System.EventArgs e)
{
	string strFilename = this.dtpFilename.Text + ".xml";
	XmlDocument docXML = new XmlDocument();
	string strContent = null;
	string strTotalOrder = this.txtTotalOrder.Text;
	string strParentOrder = null;

	if( this.chkKeepRemove1.Checked == true )
	{
		strContent = strContent +
		"<PartSold><PartNumber>" + this.txtPartNumber1.Text + "</PartNumber>" +
			"<PartName>" + this.txtPartName1.Text + "</PartName>" +
			"<UnitPrice>" + this.txtUnitPrice1.Text + "</UnitPrice>" +
			"<Qty>" + this.txtQuantity1.Text + "</Qty>" +
			"<SubTotal>" + this.txtSubTotal1.Text + "</SubTotal></PartSold>";
	}

	if( this.chkKeepRemove2.Checked == true )
	{
		strContent = strContent +
		"<PartSold><PartNumber>" + this.txtPartNumber2.Text + "</PartNumber>" +
			"<PartName>" + this.txtPartName2.Text + "</PartName>" +
			"<UnitPrice>" + this.txtUnitPrice2.Text + "</UnitPrice>" +
			"<Qty>" + this.txtQuantity2.Text + "</Qty>" +
			"<SubTotal>" + this.txtSubTotal2.Text + "</SubTotal></PartSold>";
	}

	if( this.chkKeepRemove3.Checked == true )
	{
		strContent = strContent +
		"<PartSold><PartNumber>" + this.txtPartNumber3.Text + "</PartNumber>" +
			"<PartName>" + this.txtPartName3.Text + "</PartName>" +
			"<UnitPrice>" + this.txtUnitPrice3.Text + "</UnitPrice>" +
			"<Qty>" + this.txtQuantity3.Text + "</Qty>" +
			"<SubTotal>" + this.txtSubTotal3.Text + "</SubTotal></PartSold>";
	}

	if( this.chkKeepRemove4.Checked == true )
	{
		strContent = String.Concat(strContent,
		"<PartSold><PartNumber>", this.txtPartNumber4.Text, "</PartNumber>",
			"<PartName>", this.txtPartName4.Text, "</PartName>",
			"<UnitPrice>", this.txtUnitPrice4.Text, "</UnitPrice>",
			"<Qty>", this.txtQuantity4.Text, "</Qty>",
			"<SubTotal>", this.txtSubTotal4.Text, "</SubTotal></PartSold>");
	}

	if( this.chkKeepRemove5.Checked == true )
	{
		strContent = String.Concat(strContent, 
		"<PartSold><PartNumber>", this.txtPartNumber5.Text, "</PartNumber>",
			"<PartName>", this.txtPartName5.Text, "</PartName>",
			"<UnitPrice>", this.txtUnitPrice5.Text, "</UnitPrice>",
			"<Qty>", this.txtQuantity5.Text, "</Qty>",
			"<SubTotal>", this.txtSubTotal5.Text, "</SubTotal></PartSold>");
	}

	if( this.chkKeepRemove6.Checked == true )
	{
		strContent = String.Concat(strContent, 
		"<PartSold><PartNumber>", this.txtPartNumber6.Text, "</PartNumber>",
			"<PartName>", this.txtPartName6.Text, "</PartName>",
			"<UnitPrice>", this.txtUnitPrice6.Text, "</UnitPrice>",
			"<Qty>", this.txtQuantity6.Text, "</Qty>",
			"<SubTotal>", this.txtSubTotal6.Text, "</SubTotal></PartSold>");
	}

	if( File.Exists(strFilename) )
	{
		// If the file exists already, open it
		docXML.Load(strFilename);
		// Get a reference to the root element
		XmlElement elmRoot = docXML.DocumentElement;
		// Get a reference to the last child of the root
		XmlNode nodLastOrder = elmRoot.LastChild;
		// Get the OrderNumber attribute of the last order and increment it by 1
int NewOrderNumber = int.Parse(nodLastOrder.Attributes["OrderNumber"].InnerText) + 1;

		// Create a new order as an element
		XmlElement elmNewOrder = docXML.CreateElement("Order");
		// Add its attributes
		elmNewOrder.SetAttribute("OrderNumber", NewOrderNumber.ToString());
		elmNewOrder.SetAttribute("TotalOrder", strTotalOrder);
		elmNewOrder.InnerXml = strContent;
		docXML.DocumentElement.AppendChild(elmNewOrder);
		docXML.Save(strFilename);
	}
	else
	{
		// If the file doesn't exist, get ready to create it
	strParentOrder = "<Order OrderNumber=\"1\" TotalOrder=\"" + strTotalOrder, "\">";

		// If the file doesn't exist, create it
		docXML.LoadXml("<?xml version=\"1.0\" encoding=\"utf-8\"?>" +
			"<Orders>" +
			strParentOrder + strContent + "</Order></Orders>");
		docXML.Save(strFilename);
	}

	// Reset the Order Processing form
	this.lvwAvailableParts.Items.Clear();
	this.cboCategories.SelectedIndex = -1;
	this.cboModels.SelectedIndex     = -1;
	this.cboMakes.SelectedIndex      = -1;
	this.cboYears.SelectedIndex      = -1;
	this.chkKeepRemove1.Checked = false;
	this.chkKeepRemove2.Checked = false;
	this.chkKeepRemove3.Checked = false;
	this.chkKeepRemove4.Checked = false;
	this.chkKeepRemove5.Checked = false;
	this.chkKeepRemove6.Checked = false;
	this.CalculateTotalOrder();
}