Validating a Credit Card

<?php
function ValidateCreditCardNumber($cc_num)
{
  $pattern = "/^3[47]\d{13}$/";//American Express
  if (preg_match($pattern,$cc_num))
  {
    return true;
  }
 
  $pattern = "/^([30|36|38]{2})([0-9]{12})$/";//Diner's Club
  if (preg_match($pattern,$cc_num))
  {
    return true;
  }
 
  $pattern = "/^6011\d{12}$/";//Discover Card
  if (preg_match($pattern,$cc_num))
  {
    return true;
  }
 
  $pattern = "/^5[12345]\d{14}$/";//Mastercard
  if (preg_match($pattern,$cc_num))
  {
    return true;
  }
 
  $pattern = "/^4\d{12}(\d\d\d){0,1}$/";//Visa
  if (preg_match($pattern,$cc_num))
  {
    return true;
  }
 
  $pattern = "/^30[012345]\d{11}$/";//Diners
  if (preg_match($pattern,$cc_num))
  {
    return true;
  }
 
  $pattern = "/^3[68]\d{12}$/";//Diners #2
  if (preg_match($pattern,$cc_num))
  {
    return true;
  }
 
  // Not valid
  return false; 
}
?>