Format credit card number with - hyphen

Function accepts credit card number as string parameter and formats it by adding "-" hyphen after every 4 characters.

Function

function formatCreditCard($cc) {

    $cc = str_replace(array('-', ' '), '', $cc);
    $cc_length = strlen($cc);
    $newCreditCard = substr($cc, -4);

    for ($i = $cc_length - 5; $i >= 0; $i--) {

        if ((($i + 1) - $cc_length) % 4 == 0)
            $newCreditCard = '-' . $newCreditCard;

        $newCreditCard = $cc[$i] . $newCreditCard;
    }

    return $newCreditCard;
}

Calling The Function

$string = '5555222299997777';
echo formatCreditCard($string);

Output

5555-2222-9999-7777