Example Application: Simple Interest

Description

This example explores the techniques of using the button control by adding bitmaps to them. The application is used to calculate the amount of interest accumulated on a loan.

Practical Learning: Using a Picture on a Button

1. Start Microsoft Visual Studio
2. To start a new application, on the main menu, click File -> New Project...
3. In the middle list, click Windows Application and change the Name to SimpleInterest1
4. Click OK
5. On the main menu, click Project -> Add New Item...
6. In the middle list, click Icon File
7. Change the Name to Calculator and click OK
8. Right-click a white area in the icon designer -> Delete Image Type
9. Right-click the icon designer again -> Current Icon Image Types -> 16x16, 16 colors
10. Design the icon as follows:
     
    
11. On the main menu, click Project -> Add New Item...
12. In the middle list, click Icon File and change the Name to exit
13. Click Add
14. Right-click a white area in the icon designer -> Delete Image Type
15. Right-click the icon designer again -> Current Icon Image Types -> 16x16, 16 colors
16. Design the icon as follows:
     
    
17. Save and close the icon window
18. In the Solution Explorer, right-click Form1.cs and click Rename
19. Type SimpleInterest.cs and press Enter twice
20. Design the form as follows:
     

    

    Control	Text	Name	TextAlign
    GroupBox	Loan Preparation
    Label	Principal
    TextBox	0.00	txtPrincipal	Right
    Label	Interest Rate:
    TextBox	0.00	txtInterestRate	Right
    Label	%
    Label	Periods:
    TextBox	1	txtPeriods	Right
    Label	Months
    Button	Calculate	btnCalculate
    Button	Close	btnClose
    GroupBox	Results
    Label	Interest Earned:
    TextBox	0.00	txtInterestEarned	Right
    Label	Future Value
    TextBox	0.00	txtFutureValue	Right

21. On the form, click the Calculate button
22. In the Properties window, click Image and click its ellipsis button
23. In the Select Resource dialog box, click Import
24. In the Files of Type box, select All Files
25. Locate the folder of the current project, select Calculator.ico and click Open
26. On the Select Resource dialog box, click OK
27. Change the following properties of the Calculate button:
    ImageAlign: TopCenter
    TextAlign: BottomCenter
28. On the form, click the Calculate button
29. In the Properties window, click Image and click its ellipsis button
30. In the Select Resource dialog box, click Import
31. In the Files of Type box, select All Files
32. Locate the folder of the current project, select exit.ico and click Open
33. On the Select Resource dialog box, click OK
34. Change the following properties of the Close button:
    ImageAlign: TopCenter
    TextAlign: BottomCenter
     
    
35. On the form, double-click the Calculate button and implement its Click event as follows:
    

    private void btnCalculate_Click(object sender, EventArgs e)
    {
            decimal Principal    = 0.00M,
                        InterestRate = 0.00M,
                        InterestEarned,
                        FutureValue;
            decimal Periods = 0.00M;
    
            try
            {
                    Principal = decimal.Parse(txtPrincipal.Text);
            }
            catch (FormatException)
            {
                    MessageBox.Show("The value you entered for the " +
                                    "principal is not valid");
            }
    
            try
            {
                    InterestRate = decimal.Parse(txtInterestRate.Text);
            }
            catch (FormatException)
            {
                    MessageBox.Show("Wrong Value: The interest rate must " +
                                    "be a value between 0 and 100");
            }
    
            try
            {
                    Periods = decimal.Parse(txtPeriods.Text);
            }
            catch (FormatException)
            {
                    MessageBox.Show("You entered an invalid value for the periods");
            }
    
            decimal I = InterestRate / 100;
            decimal p = Periods / 12;
            InterestEarned = Principal * I  * p;
            FutureValue    = Principal + InterestEarned;
    
            txtInterestEarned.Text = InterestEarned.ToString("C");
            txtFutureValue.Text = FutureValue.ToString("C");
    }

36. Return to the form
37. On the form, double-click the Close button and implement its Click event as follows:
    

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

38. Execute the application and test the calculation
     
    
39. Close the form and return to your programming environment