php信用卡卡号验证函数

介绍一个php信用卡卡号验证函数，可以验证一个卡号是否是信用卡。

function validateCard ($cardnumber){
    $cardnumber = preg_replace ("/D|s/","", $cardnumber);
    $cardlength = strlen($cardnumber);if($cardlength !=0){
        $parity = $cardlength %2;
        $sum =0;for($i=0; $i<$cardlength; $i++){
            $digit = $cardnumber[$i];if($i %2== $parity) $digit = $digit *2;if($digit >9) $digit = $digit -9;
            $sum = $sum + $digit;}
        $valid =($sum %10==0);return $valid;}returnfalse;}

文章摘自：php信用卡卡号验证函数