Credit Card Number Validation

Credit Card Number Validation

this function takes a string of the cardnumber with no blanks, and returns true if the number validates as a creditcard number, else it returns false.

PHP Example:

PHP code:

function validate_cardnum($cardnum)
{
$checkdigit=substr($cardnum,-1);
$remainingcardnum=substr($cardnum,0,strlen($cardnum)-1);

$i=0;

while($i < strlen($remainingcardnum))
{
if($i%2==0)
$remaing_array[$i]=substr($remainingcardnum,($i+1)*-1,1) * 2;
else
$remaing_array[$i]=substr($remainingcardnum,($i+1)*-1,1);

if($remaing_array[$i]>=10)
$checksum=$checksum+1;

$checksum=$checksum+($remaing_array[$i]%10);
$i++;
}

$calculatedcheckdigit=(10-($checksum%10))%10;
if( $calculatedcheckdigit==$checkdigit)
return true;
else
return false;
}

This is excellent. I actually have use for this as a pre-screen on a sales site I am contracted on. Thanks for sharing the code. Do all cards use the same formula for validation?

I think this formula will aplly to all credit cards and we can say it some universal type of coding to handle all cards .is not it?

I'm curious how this works. It appears to just make sure they are all numeric and enough of them? But the ones I've seen *used* seem to check deeper than that - to see if the first four digits are a valid card starter, I think...

What exactly does the code above *do*?

i need to know ho do i get the knowledge that my creditcard has been vilidated?

How do u validated the whether the card is fake or not even if its number matched with credit card

Nice less of a chance of fraud. I'm gonna play with this script =]

@Michael: this only looks and see if the fields are filled in. This is just a snippet, you must have a bigger script or something to record the numbers to a secure database. So you can check them later with a machine or a site like PayPal to get your payment. It will tell you if it's really been "validated"

@mtajim: You don't until you charge the card.

i believe the first 4 numbers correlate to the respective CC company.