When you have finished the steps in the book, then carry out the following to final solution:

Display the results below the form instead of on a separate page.

After each calculation, set the values in the text boxes to empty strings

display_result.php

// validate investment if ($investment === FALSE ) { $error_message = 'Investment must be a valid number.'; } else if ( $investment <= 0 ) { $error_message = 'Investment must be greater than zero.'; // validate interest rate } else if ( $interest_rate === FALSE ) { $error_message = 'Interest rate must be a valid number.'; } else if ( $interest_rate <= 0 ) { $error_message = 'Interest rate must be greater than zero.'; } else if ($interest_rate > 15) { $error_message = 'Interest rate must be less than or equal to 15.'; } // validate years } else if ( $years === FALSE ) { $error_message = 'Years must be a valid whole number.'; } else if ( $years <= 0 ) { $error_message = 'Years must be greater than zero.'; } else if ( $years > 30 ) { $error_message = 'Years must be less than 31.'; // set error message to empty string if no invalid entries } else { $error_message = ''; }

// if an error message exists, go to the index page if ($error_message != '') { include('index.php'); exit(); }

// calculate the future value $future_value = $investment; for ($i = 1; $i <= $years; $i++) { $future_value = $future_value + ($future_value * $interest_rate * .01); }

// apply currency and percent formatting $investment_f = '$'.number_format($investment, 2); $yearly_rate_f = $interest_rate.'%'; $future_value_f = '$'.number_format($future_value, 2); ?>

Future Value Calculator

Investment Amount:

Yearly Interest Rate:

Number of Years:

Future Value:

This calulation was done on .

index.php

Future Value Calculator

Investment Amount:

Yearly Interest Rate:

Number of Years: