php script calculator

$page_title = 'Widget Cost Calculator';
include ('../includes/header.html');

// This function calculates the total and prints the results. We have made the $tax argument optional for the user. It now has a default value.

function calculate_total ($qty, $cost, $tax = 5) {
       
        $total = ($qty * $cost);
        $taxrate = ($tax / 100); // Turns 5% into 05.
        $total += ($total * $taxrate); // Add the tax
       
        return number_format($total, 2);
       
} // end of function

// Check the form submission
if (isset($_POST['submitted'])) {
       
        // Minimal form submission
        if ( is_numeric($_POST['quantity']) && is_numeric($_POST['price']) ) {
               
                // Print the heading
                echo '

Total Cost

';
               
                // Call the function with or without tax:
               
                if (is_numeric($_POST['tax'])) {
                        $sum = calculate_total ($_POST['quantity'], $_POST['price'], $_POST['tax']);
                } else {
                        $sum = calculate_total ($_POST['quantity'], $_POST['price']);
                }
               
                // print the results:
                echo 'The total cost of purchasing ' . $_POST['quantity'] . ' Widget(s) at £' . number_format ($_POST['price'], 2) . ' each, with tax, is £' . $sum . '.
';
                       
        } else { // invalid submitted values:
        echo '

Error!

       

Please enter a valid quantity and price.

';
        }
       
} // end of main isset() IF.

// Leave the PHP section and create the HTML form:
?>

Widget Cost Calculator

Quantity:
Price:

Tax (%): (Optional)

include ('../includes/footer.html');

?>