Snippit: PHP: Simple US Zip Code format validation

gistfile1.php

<?php
/* Validates if $zipCode is a 5 digit number in the 12345 format. Note that this simply checks to see if $zipCode is a 5 digit number, not necessarily a valid U.S. Zip Code.
*/
function validateZipCode($zipCode) {
if (preg_match('#[0-9]{5}#', $zipCode))
	return true;
else
	return false;
}
?>

private function isValidZipCode($zipCode) {
	return (preg_match('#[0-9]{5}#', $zipCode)) ? true : false;
}

tweaked a bit and it finally worked for me and includes the optional zip+4 validation if a user decides to include that

function isValidZipCode($zipCode) {
    return (preg_match('/^[0-9]{5}(-[0-9]{4})?$/', $zipCode)) ? true : false;
}

check it out here (changed the return from bool to string in this demo): https://repl.it/repls/NativeCornyProject

what bout to add empty zipcode