Write the code that gets and displays the data entered by the user

1. Open the index.php file for this application and review the code. Note the names that are used for the three text boxes.

2. Modify the code so it uses drop-down lists instead of text boxes for the first two entries.

3. For the investment amount, the drop-down list should display values from 10,000 to 50,000 incremented by 5,000. To do this, you can use a for loop that creates the HTML for the drop-down list.

If you have any trouble with this, you may want to look ahead to the last example in figure 8-11 of the next chapter. Or, you can come back to this after you read chapter 8.

4. For the yearly interest rate, the drop-down list should display values from 4 to 12 incremented by .5.

5. Test the application to make sure it works correctly.

display_results.php

// get the data from the form

$investment = filter_input(INPUT_POST, 'investment',

FILTER_VALIDATE_FLOAT);

$interest_rate = filter_input(INPUT_POST, 'interest_rate',

FILTER_VALIDATE_FLOAT);

$years = filter_input(INPUT_POST, 'years',

FILTER_VALIDATE_INT);

// 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.';

// 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:

index.php

//set default value of variables for initial page load

if (!isset($investment)) { $investment = '10000'; }

if (!isset($interest_rate)) { $interest_rate = '5'; }

if (!isset($years)) { $years = '5'; }

?>

Future Value Calculator

Investment Amount:

value=""/>

Yearly Interest Rate:

value=""/>

Number of Years:

value=""/>