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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.
  

ApplicationApplication: Introducing the Application
  1. Start a new Window Application named SimpleInterest2
  2. Design the form as follows:
     
    Simple Interest
    Control Text Name TextAlign
    GroupBox GroupBox Loan Preparation    
    Label Label Principal    
    TextBox TextBox 0.00 txtPrincipal Right
    Label Label Interest Rate:    
    TextBox TextBox 0.00 txtInterestRate Right
    Label Label %    
    Label Label Loan Start Date:    
    DateTimePicker DateTimePicker   dtpStartDate  
    Label Label Loan End Date:    
    DateTimePicker DateTimePicker   dtpLoandEndDate  
    Label Label Periods:    
    TextBox TextBox 1 txtPeriods Right
    Label Label days    
    Button Button Calculate btnCalculate  
    GroupBox GroupBox Results    
    Label Label Interest Earned:    
    TextBox TextBox 0.00 txtInterestEarned Right
    Label Label Future Value:    
    TextBox TextBox 0.00 txtFutureValue Right
    Button 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 Properties
  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
 
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