Example Application: Simple Interest

Description

The date/time picker control provides a convenient way to select a date to use in an application. This reduces the likelihood of mistakes. To illustrate it, we will create an application that calculates the values of an interest paid on a loan.

Practical Learning: Introducing the Application

1. Start a new Window Application named SimpleInterest2
2. 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		Loan Start Date:
   DateTimePicker			dtpStartDate
   Label		Loan End Date:
   DateTimePicker			dtpLoandEndDate
   Label		Periods:
   TextBox		1	txtPeriods	Right
   Label		days
   Button		Calculate	btnCalculate
   GroupBox		Results
   Label		Interest Earned:
   TextBox		0.00	txtInterestEarned	Right
   Label		Future Value:
   TextBox		0.00	txtFutureValue	Right
   Button		Close	btnClose

3. On the form, click the dtdEndDate date picker control
4. In the Properties window, click the Events button and double-click CloseUp to generate its event
5. Implement the event as follows:
   

   private void dtpEndDate_CloseUp(object sender, EventArgs e)
   {
               double Principal = 0.00D,
                      InterestRate = 0.00D,
                      Periods = 0.00D;
               double InterestEarned, FutureValue;
               DateTime StartDate, EndDate;
               TimeSpan spnPeriods;
   
               // Get the value of the principal
               try
               {
                   Principal = double.Parse(txtPrincipal.Text);
               }
               catch (FormatException)
               {
                   MessageBox.Show("Invalid Principal Value");
               }
   
               // Get the interest rate
               try
               {
                   InterestRate  = double.Parse(txtInterestRate.Text) / 100;
               }
               catch (FormatException)
               {
                   MessageBox.Show("Invalid Interest Rate");
               }
   
               // Get the start and end dates
               StartDate = dtpStartDate.Value;
               EndDate = dtpEndDate.Value;
   
               // Make sure the end date doesn't occur before the start date
               if (EndDate < StartDate)
               {
                   MessageBox.Show("Invalid Date Sequence: " +
                                   "the end date must occur after the start date");
                   dtpEndDate.Value = DateTime.Today;
                   return;
               }
   
               // Get the difference in days
               // The will be the periods
               spnPeriods = EndDate.Subtract(StartDate);
               int days = spnPeriods.Days;
               txtPeriods.Text = days.ToString();
               double p = 0.00D;
   
               // Because we will allow the user to directly specify 
               // the number of days, let's get the period from its text box
               try
               {
                   p = double.Parse(txtPeriods.Text);
               }
               catch (FormatException)
               {
                   MessageBox.Show("Invalid number of days");
               }
   
               // The actual period is gotten as follows
               Periods = p / 365;
               // Now we can perform the calculations
               InterestEarned = Principal * InterestRate * Periods;
               FutureValue = Principal + InterestEarned;
   
               // Display the values
               txtInterestEarned.Text = InterestEarned.ToString("C");
               txtFutureValue.Text = FutureValue.ToString("C");
   }

6. Return to the form and click the Periods text box
7. From the Events section of the Properties window, double-click Leave
8. Implement the event as follows:
   

   private void txtPeriods_Leave(object sender, EventArgs e)
   {
           // If the user directly enters the number of days
           // in the Periods text box and press Tab,
           // we can perform the caltulation
           dtpEndDate_CloseUp(sender, e);
   }

9. Return to the form and double-click the Calculate button
10. Implement the event as follows:
    

    private void btnCalculate_Click(object sender, EventArgs e)
    {
            // If the user directly enters the number of days
            // in the Periods text box and clicks the Calculate
            // button, we can perform the caltulation
            dtpEndDate_CloseUp(sender, e);
    }

11. Return to the form and double-click the Close button
12. Implement the event as follows:
    

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

13. Return to the form
14. In the Properties window, click the Properties button
15. On the form, click the top date picker control
16. In the Properties window, change the following values:
    CalendarForeColor: Blue
    CalendarMonthBackground: SkyBlue
    CalendarTitleBackColor: Navy
    CalendarTitleForeColor: Gold
    CalendarTrailingForeColor: DodgeBlue
17. On the form, click the top date picker control
18. In the Properties window, change the following values:
    CalendarForeColor: Maroon
    CalendarMonthBackground: Orange
    CalendarTitleBackColor: Sienna
    CalendarTitleForeColor: Khaki
    CalendarTrailingForeColor: White
19. Execute the application and test the application
     

    

    

    

20. Close the form and return to your programming environment