Example Application - Watts A Loan: Loan Preparation

	Watts A Loan: Loan Preparation

Watts A Loan - Loan Preparation

Introduction

Imagine you are asked to create an application for a company that is in the business of lending money, including personal loans (cash loan), car loans, furniture loans, music instrument loans, etc. One of the actions you would take consists of creating a form that an employee can use to prepare a loan presented to a customer. This is the type of example application we will create.

To implement our application, we will use the Visual Basic library to calculate the monthly payment that will be applied to the loan. This will be a file-based application. For this reason, we will create a file to store the information related to a loan.

Practical Learning: Creating the Application

Start Microsoft Visual C# Professional or Microsoft Visual C# 2005 Express Edition
To create a new application, on the main menu, click File -> New -> Project...
In the Templates list, click Windows Application
Set the name to WattsALoan2 and click OK
In the Solution Explorer, right-click Form1.cs and click Rename
Type LoanPreparation.cs and press Enter

To create a new form, on the main menu, click Project -> Add Windows Form...

In the Templates list, make sure Windows Form is selected.
Set the Name to NewEmployee and click Add

Design the form as follows:

Control	Text	Name
Label	Employee #:
TextBox		txtEmployeeNumber
Label	Employee Name:
TextBox		txtEmployeeName
Button	Create	btnCreate
Button	Close	btnClose

Double-click the Close button and change the file as follows:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.IO;

namespace WattsALoan2b
{
    public partial class NewEmployee : Form
    {
        public NewEmployee()
        {
            InitializeComponent();
        }

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

Return to the NewEmployee form and double-click its Create button

Implement its Click event as follows:

private void btnCreate_Click(object sender, EventArgs e)
{
            string strFilename = @"C:\Watts A Loan\Employees.wal";
            FileInfo fiEmployees = new FileInfo(strFilename);
            StreamWriter stwEmployees = null;

            // Normally, we should have the file already but just in case...
            if (!fiEmployees.Exists)
                stwEmployees = fiEmployees.CreateText();
            else // If the file exists already, then we will only add to it
                stwEmployees = fiEmployees.AppendText();

            try
            {
                stwEmployees.WriteLine(txtEmployeeNumber.Text);
                stwEmployees.WriteLine(txtEmployeeName.Text);
            }
            finally
            {
                stwEmployees.Close();
            }

            txtEmployeeNumber.Text = "";
            txtEmployeeName.Text = "";
            txtEmployeeNumber.Focus();
}

To be able to use the Visual Basic library, in the Solution Explorer, right-click References and click Add Reference...
In the .NET property page, click Microsoft.VisualBasic
Click OK
Display the LoanPreparation form
In the Common Controls section of the Toolbox, click ToolTip and click the form

Design the form as follows:

Control	Name	Text	ToolTip on toolTip1
Label		If this is a new loan, enter a new account number and the name of the customer who is requesting the loan
Label		To open a previously prepared loan, enter its account number and press Tab
Label		Acnt #:
Label		Customer Name:
Label		Customer:
TextBox	txtAccountNumber		Account number of the customer requesting the loan
TextBox	txtCustomerName		Name of the customer requesting the loan
Label		Empl #:
Label		Employee Name:
Label		Prepared By:
TextBox	txtEmployeeNumber		Employee number of the clerk preparing the loan
TextBox	txtEmployeeName		Name of the clerk preparing the loan
Button	btnNewEmployee		Used to add a new employee to the company
Button	btnNewCustomer		Used to create an account for a new customer
Label		Loan Amount:
TextBox	txtLoanAmount		Amount of loan the customer is requesting
Label		Interest Rate:
TextBox	txtInterestRate		Annual percentage rate of the loan
Label		%
Label		Periods
TextBox		txtPeriods	The number of months the loan is supposed to last
Button	btnCalculate	Calculate	Used to calculate the monthly payment
Label		Monthly Payment:
TextBox	txtMonthlyPayment		The minimum amount the customer should pay every month
Button	btnClose	Close	Used to close the form

Double-click the Calculate button and implement its event as follows:

private void btnCalculate_Click(object sender, EventArgs e)
{
    double LoanAmount = 0.00D, MonthlyPayment = 0.00D;
    double InterestRate = 0.00D, Periods = 0.00D;

            try
            {
                LoanAmount = double.Parse(txtLoanAmount.Text);
            }
            catch (FormatException)
            {
                MessageBox.Show("Invalid Loan Amount");
            }

            try
            {
                InterestRate = double.Parse(txtInterestRate.Text);
            }
            catch (FormatException)
            {
                MessageBox.Show("Invalid Interest Rate");
            }

            try
            {
                Periods = double.Parse(txtPeriods.Text);
            }
            catch (FormatException)
            {
                MessageBox.Show("Invalid Periods Value");
            }

            try
            {
                MonthlyPayment =
                    Microsoft.VisualBasic.Financial.Pmt(
                       InterestRate / 12 / 100,
                           Periods,
                       -LoanAmount,
                       0,
                   Microsoft.VisualBasic.DueDate.BegOfPeriod);
                txtMonthlyPayment.Text = MonthlyPayment.ToString("F");
            }
            catch (FormatException)
            {
                MessageBox.Show("Invalid Periods Value");
            }
        }

Return to the form and double-click the Close button to implement its event as follows:
private void btnClose_Click(object sender, EventArgs e) { Close(); }
Scroll up completely and, under the other using lines, type using System.IO;
Access the LoanPresentation form

Double-click the New button on the form and implement the event as follows:

private void btnNewEmployee_Click(object sender, EventArgs e)
{
    NewEmployee frmNewEmployee = new NewEmployee();

    frmNewEmployee.ShowDialog();
}

Return to the form
On the LoanPreparation form, double-click an unoccupied area of its body

Implement its Load event as follows:

private void LoanPresentation_Load(object sender, EventArgs e)
{
            string strDirectory = @"C:\Watts A Loan";

            if (!Directory.Exists(strDirectory))
                Directory.CreateDirectory(strDirectory);

            string strFilename = strDirectory + @"\Employees.wal";

            FileInfo fiEmployees = new FileInfo(strFilename);

            // If the employees file was not created already,
            // then create it
            if (!fiEmployees.Exists)
            {
                StreamWriter stwEmployees = fiEmployees.CreateText();

                // And create a John Doe employee
                try
                {
                    stwEmployees.WriteLine("00-000");
                    stwEmployees.WriteLine("John Doe");
                }
                finally
                {
                    stwEmployees.Close();
                }
            }
}

Return to the LoanPreparation form
In the combo box on top of the Properties window, select txtAccountNumber

In the Events section, double-click Leave and implement the event as follows:

private void txtAccountNumber_Leave(object sender, EventArgs e)
{
    string strPath = @"C:\Watts A Loan";

    DirectoryInfo diLoans = new DirectoryInfo(strPath);
    FileInfo[] aryLoans = diLoans.GetFiles("*", 
					SearchOption.AllDirectories);

            string strFilename = txtAccountNumber.Text + ".wal";
            string strFullname = strPath + "none.wal";
            bool found = false;

            foreach (FileInfo fle in aryLoans)
            {
                if (fle.Name == strFilename)
                {
                    found = true;
                    strFullname = fle.FullName;
                }
            }

            if (found == true)
            {
                FileStream stmLoans =
                    File.Open(strFullname,
                                FileMode.Open,
                                FileAccess.Read);
                BinaryReader bnrLoans = new BinaryReader(stmLoans);

                txtAccountNumber.Text = bnrLoans.ReadString();
                txtCustomerName.Text = bnrLoans.ReadString();
                txtEmployeeNumber.Text = bnrLoans.ReadString();
                txtEmployeeName.Text = bnrLoans.ReadString();
                txtLoanAmount.Text = bnrLoans.ReadString();
                txtInterestRate.Text = bnrLoans.ReadString();
                txtPeriods.Text = bnrLoans.ReadString();
                txtMonthlyPayment.Text = bnrLoans.ReadString();

                bnrLoans.Close();
                stmLoans.Close();
            }
}

In the combo box on top of the Properties window, select txtEmployeeNumber
On the Properties window, click the Events button and double-click Leave

Implement the event as follows:

private void txtEmployeeNumber_Leave(object sender, EventArgs e)
{
    string strFilename = @"C:\Watts A Loan\Employees.wal";
    FileInfo fiEmployees = new FileInfo(strFilename);

    if (fiEmployees.Exists)
    {
        if (txtEmployeeNumber.Text == "")
        {
            txtEmployeeName.Text = "";
            return;
        }
        else
        {
            StreamReader strEmployees = fiEmployees.OpenText();
            string strEmployeeNumber, strEmployeeName;
            bool found = false;

            try
            {
                while( (strEmployeeNumber = strEmployees.ReadLine()) != null )
                {
                    if (strEmployeeNumber == txtEmployeeNumber.Text)
                    {
                        strEmployeeName = strEmployees.ReadLine();
                        txtEmployeeName.Text = strEmployeeName;
                        found = true;
                    }
                }

                // When the application has finished checking the file
                // if there was no employee with that number, 
                // let the user know
                if (found == false)
                {
                    MessageBox.Show("No employee with that number was found");
                    txtEmployeeName.Text = "";
                    txtEmployeeNumber.Focus();
                }
            }
            finally
            {
                strEmployees.Close();
            }
        }
    }
}

Return to the form and double-click the Save button

Implement the event as follows:

private void btnSave_Click(object sender, EventArgs e)
{
    string strPath = @"C:\Watts A Loan\" + txtAccountNumber.Text + ".wal";

    FileStream stmLoan = File.Create(strPath);
    BinaryWriter bnwLoan = new BinaryWriter(stmLoan);

    bnwLoan.Write(txtAccountNumber.Text);
    bnwLoan.Write(txtCustomerName.Text);
    bnwLoan.Write(txtEmployeeNumber.Text);
    bnwLoan.Write(txtEmployeeName.Text);
    bnwLoan.Write(txtLoanAmount.Text);
    bnwLoan.Write(txtInterestRate.Text);
    bnwLoan.Write(txtPeriods.Text);
    bnwLoan.Write(txtMonthlyPayment.Text);

    txtAccountNumber.Text = "";
    txtCustomerName.Text = "";
    txtEmployeeNumber.Text = "";
    txtEmployeeName.Text = "";
    txtLoanAmount.Text = "";
    txtInterestRate.Text = "";
    txtPeriods.Text = "";
    txtMonthlyPayment.Text = "";

    txtAccountNumber.Focus();

    bnwLoan.Close();
    stmLoan.Close();
}

Execute the application to test it

First create a few employees as follows:

Employee #	Employee Name
42-806	Patricia Katts
75-148	Helene Mukoko
36-222	Frank Leandro
42-808	Gertrude Monay

Process a few loans
Close the application


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