Here's the code:

Cecil

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

namespace CarCareCenter
{
public partial class CarCareForm : Form
{
private const decimal
decStereoSystem = 425.76M,
decLeatherInterior = 987.41M,
decComputerNavigation = 1741.23M,
decStandardFinish = 0M,
decPearlizeFinish = 345.72M,
decCustomizedDetailing = 599.99M,
decTaxRate = 0.08M;

private decimal decTradeInAllowance = 0, decSubTotal = 0,
decSalesTax = 0, decAmountDue = 0, decAccessoriesTotal = 0;

public CarCareForm()
{
InitializeComponent();
}

private void CarCareForm_Load(object sender, EventArgs e)
{

}

private void exitButton_Click(object sender, EventArgs e)
{
this.Close();
}

private void clearButton_Click(object sender, EventArgs e)
{
this.accessoriesLabel.Text = "";
this.salesTaxLabel.Text = "";
this.basePriceTextBox.Text = "";
this.tradeInAllowanceTextBox.Text = "";
this.stereoCheckBox.Checked = false;
this.leatherInteriorCheckBox.Checked = false;
this.computerNavigationCheckBox.Checked = false;
this.subTotalLabel.Text = "";
this.amountDueLabel.Text = "";
//Clear variables.
decSubTotal = 0;
decAccessoriesTotal = 0;
decAmountDue = 0;
decSalesTax = 0;
decTradeInAllowance = 0;
disableControls();
//Put the focus on the first text box.
this.basePriceTextBox.Focus();
}

private void calculateButton_Click(object sender, EventArgs e)
{
string strMessageString="";

//Calculate the cost of the vehicle.
if (this.basePriceTextBox.Text != "")
{
//Convert from Text to Decimal value.
decSubTotal = decimal.Parse(this.basePriceTextBox.Text);
// Types of Interiors using check boxes. See which ones were checked.
if (this.stereoCheckBox.Checked)
{
decAccessoriesTotal += decStereoSystem;
}
if (this.leatherInteriorCheckBox.Checked)
{
decAccessoriesTotal += decLeatherInterior;
}
if (this.computerNavigationCheckBox.Checked)
{
decAccessoriesTotal += decComputerNavigation;
}
decSubTotal += decAccessoriesTotal;

//Types of Finishes. See which Radio Button is checked.
if (this.standardFinishRadioButton.Checked)
{
decSubTotal += decStandardFinish;
}
else if (this.pearlizedFinishRadioButton.Checked)
{
decSubTotal += decPearlizeFinish;
}
else if (this.customizedDetailingRadioButton.Checked)
{
decSubTotal += decCustomizedDetailing;
}
// Determine the taxes prior to deducting the trade-in value.
decSalesTax = (decSubTotal * decTaxRate);
//Add the sales tax to the subTotal variable.
decSubTotal += decSalesTax;

//See if the Buyer has a trade-in. Enter the value.
if (this.tradeInAllowanceTextBox.Text != "")
{
decTradeInAllowance =
decimal.Parse(this.tradeInAllowanceTextBox.Text);
decAmountDue = (decSubTotal - decTradeInAllowance);
}
//In the case that there is no value in the Trade-In Allowance textbox.
else
{
decAmountDue += decSubTotal;
}

//Now, display the results in the Labels.
this.accessoriesLabel.Text = decAccessoriesTotal.ToString("C");
this.salesTaxLabel.Text = decSalesTax.ToString("C");
this.subTotalLabel.Text = decSubTotal.ToString("C");
this.amountDueLabel.Text = decAmountDue.ToString("C");
this.calculateButton.Enabled = false;
}
}

private void basePriceTextBox_Leave(object sender, EventArgs e)
{
/*
string strMessageForBasePrice="";
try
{
if (decimal.Parse(this.basePriceTextBox.Text) >= 1)
{
enableControls();
this.tradeInAllowanceTextBox.Focus();
}
if (decimal.Parse(this.basePriceTextBox.Text) < 1)
{
disableControls();
}
}
catch (FormatException err)
{
strMessageForBasePrice =
"Non-numeric value was entered for Base Price";
MessageBox.Show(strMessageForBasePrice + ". " + err.Message,
"Data Entry Error",
MessageBoxButtons.OK, MessageBoxIcon.Information);
}*/
}
//Rather than repeat the below code several times, I decided to create a method.
private void disableControls()
{
this.stereoCheckBox.Enabled = false;
this.leatherInteriorCheckBox.Enabled = false;
this.computerNavigationCheckBox.Enabled = false;
this.standardFinishRadioButton.Enabled = false;
this.pearlizedFinishRadioButton.Enabled = false;
this.customizedDetailingRadioButton.Enabled = false;
this.tradeInAllowanceTextBox.Enabled = false;
this.calculateButton.Enabled = false;
}

private void enableControls()
{
this.stereoCheckBox.Enabled = true;
this.leatherInteriorCheckBox.Enabled = true;
this.computerNavigationCheckBox.Enabled = true;
this.standardFinishRadioButton.Enabled = true;
this.pearlizedFinishRadioButton.Enabled = true;
this.customizedDetailingRadioButton.Enabled = true;
this.tradeInAllowanceTextBox.Enabled = true;
this.calculateButton.Enabled = true;
}

private void basePriceTextBox_Validating(object sender, CancelEventArgs e)
{
string strMessageForBasePrice = "";
try
{
if (decimal.Parse(this.basePriceTextBox.Text) >= 1)
{
enableControls();
this.tradeInAllowanceTextBox.Focus();
}
if (decimal.Parse(this.basePriceTextBox.Text) < 1)
{
disableControls();
}
}
catch (FormatException err)
{
strMessageForBasePrice =
"Non-numeric value was entered for Base Price";
MessageBox.Show(strMessageForBasePrice + ". " + err.Message,
"Data Entry Error",
MessageBoxButtons.OK, MessageBoxIcon.Information);
}
}
}
}