Similar functions?

Can anyone tell me if there are similar functions in php as javascript isNaN, or do I just have to do a if (preg_match('/([A-Z][a-z][`~!@#$%^&*()_=+|\?/><,.;:{}-])/', $_POST['Personal_Hotel_CC_Number']) == 0){} I know the above doesn't work, would there be an easier way for me to find if any of the chars are not numbers? I could do: if (preg_match_all("/([0-9])/", $var, $match) == 16){} But AMEX cards are only 15 digits... It's for credit card verification. Thanks, Jake McHenry Nittany Travel MIS Coordinator http://www.nittanytravel.com