Example Application: Compounded Interest

Introduction to Radio Buttons

Description

The compounded interest is the amount of money paid as interest on a loan. This example uses some radio buttons to let the user select the frequency by which to perform the calculation.

	P = Principal
	r = Annual (Interest) Rate
	m = Number of Compounding Periods per Year
	n = Total Number of Compounding Periods
	A = Amount Earned After n periods

Application: Creating the Application

1. Start a new Windows Application named CompoundedInterest
2. Design the form as followed:
    

   

   Control		Name	Text	Additional Properties
   GroupBox			Loan Setup
   Label			Principal:
   TextBox		txtPrincipal	0.00	TextAlign: Right
   Label			Interest Rate:
   TextBox		txtInterestRate	8.25	TextAlign: Right
   Label			%
   Label			Number of Periods:
   TextBox		txtPeriods	1	TextAlign: Text
   Label			years
   GroupBox			Compound Frequency
   RadioButton		rdoMonthly
   RadioButton		rdoQuarterly
   RadioButton		rdoSemiannually
   RadioButton		rdoAnnually
   GroupBox			Results
   Label			Interest Earned:
   TextBox		txtInterestEarned	0.00	TextAlign: Right ReadOnly: True
   Label			Amount Earned:
   TextBox		txtFutureValue	0.00	TextAlign: Right ReadOnly: True
   Button		btnCalculate	Calculate
   Button		btnClose	Close

3. On the form, double-click the Close button and implement its OnClick() event as follows:
   

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

4. To test the application, press F5
5. Close the form and return to your programming environment
6. On the form, click Monthly
7. In the Properties window, double-click Checked to set its value to True
8. On the form, double-click the Calculate button and implement its Click() event as follows:
   

   private void btnCalculate_Click(object sender, EventArgs e)
   {
       double principal = 0.00,
              interestRate = 0.00,
              interestEarned = 0.00;
       double futureValue = 0.00,
              ratePerPeriod = 0.00,
              periods = 0;
       int compoundType = 0;
   
       // Retrieve the value of the principal
       principal = double.Parse(txtPrincipal.Text);
   
       // Retrieve the interest rate
       interestRate = double.Parse(txtInterestRate.Text) / 100;
   
       // Find out what radio button was clicked to apply the compound frequency
       if (rdoMonthly.Checked)
           compoundType = 12;
       else if (rdoQuarterly.Checked)
           compoundType = 4;
       else if (rdoSemiannually.Checked)
           compoundType = 2;
       else
           compoundType = 1;
   
       // Get the number of periods
       periods = double.Parse(txtPeriods.Text);
   
       // These values will make the calculation easier to read
       double i = interestRate / compoundType;
       double n = compoundType * periods;
   
       // Perform the necessary calculations
       ratePerPeriod = interestRate / periods;
       futureValue = principal * Math.Pow(1 + i, n);
       interestEarned = futureValue - principal;
   
       // Display the values in the appropriate text boxes
       txtInterestEarned.Text = interestEarned.ToString("C");
       txtFutureValue.Text = futureValue.ToString("C");
   }

9. Test the application
    
   
10. After using it, close the form and return to your programming environment