Online PHP editor | refs for GBErc

<?php $prefix = (string) 1234; $id = (string) 3; $number = $prefix . str_repeat('0', 12 - strlen($prefix) - strlen($id)) . $id; echo $number; $odd = true; $checksum = 0; $key = range(0, 9); for ($i = strlen($number); $i > 0; $i--) { if ($odd) { $odd = false; $multiplier = 3; } else { $odd = true; $multiplier = 1; } $checksum += $key[$number[$i - 1]] * $multiplier; } $checksum = 10 - $checksum % 10; $checksum = ($checksum == 10) ? 0 : $checksum; echo $checksum;