I am needing help with a credit card validation script. I have figured out how to determine if a credit card is valid/invalid but what I am needing is this:
If someone enters an invalid credit card number, is there a way to determine which number is invalid? If so, please show me how :D. Here is my current code to determine if a card is valid/invalid:
function validateCreditcard_number($credit_card_number) {
//Get the first digit
$firstnumber = substr($credit_card_number, 0, 1);
//Make sure it is the correct amount of digits. Account for dashes being present.
switch ($firstnumber) {
case 3:
if (!preg_match('/^3\d{3}[ \-]?\d{6}[ \-]?\d{5}$/', $credit_card_number)) {
return '<li>This is not a valid American Express card number. Please use a different credit/debit card or re-enter your credit/debit card details.</li>';
}
break;
case 4:
if (!preg_match('/^4\d{3}[ \-]?\d{4}[ \-]?\d{4}[ \-]?\d{4}$/', $credit_card_number)) {
return '<li>This is not a valid Visa card number. Please use a different credit/debit card or re-enter your credit/debit card details.</li>';
}
break;
case 5:
if (!preg_match('/^5\d{3}[ \-]?\d{4}[ \-]?\d{4}[ \-]?\d{4}$/', $credit_card_number)) {
return '<li>This is not a valid MasterCard card number. Please use a different credit/debit card or re-enter your credit/debit card details.</li>';
}
break;
case 6:
if (!preg_match('/^6011[ \-]?\d{4}[ \-]?\d{4}[ \-]?\d{4}$/', $credit_card_number)) {
return '<li>This is not a valid Discover card number. Please use a different credit/debit card or re-enter your credit/debit card details.</li>';
}
break;
default:
return '<li>This is not a valid credit card number. Please use a different credit/debit card or re-enter your credit/debit card details.</li>';
} //END Switch statement
//Luhn Algorithm
$credit_card_number = str_replace('.', '', $credit_card_number);
$credit_card_number = str_replace('-', '', $credit_card_number);
$credit_card_number = str_replace(' ', '', $credit_card_number);
$map = array(0, 1, 2, 3, 4, 5, 6, 7, 8, 9,
0, 2, 4, 6, 8, 1, 3, 5, 7, 9);
$sum = 0;
$last = strlen($credit_card_number) - 1;
for ($i = 0; $i <= $last; $i++) {
$sum += $map[$credit_card_number[$last - $i] + ($i & 1) * 10];
}
if ($sum % 10 != 0) {
return '<li>This is not a valid credit card number. Please use a different credit/debit card or re-enter your credit/debit card details.</li>';
} else {
//If we made it this far the credit card number is in a valid format
return 'This is a valid credit card number' ;
}
} //END validateCreditcard_number
