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


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