Example Application: Compound Interest

	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

Start a new Windows Application named CompoundedInterest

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

On the form, double-click the Close button and implement its OnClick() event as follows:
```
private void btnClose_Click(object sender, EventArgs e)
{
            Close();
}
```
To test the application, press F5
Close the form and return to your programming environment
On the form, click Monthly
In the Properties window, double-click Checked to set its value to True

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");
}

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


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