PHP函數驗證信用卡卡號是否正確

本文主要和大家分享PHP函數驗證信用卡卡號是否正確，希望能協助到大家。

function validateCard ( $cardnumber )     {        $cardnumber = preg_replace ( " /\D|\s/ " , "" , $cardnumber ) ; # strip any non-digits        $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 ;       }        return false ;    }