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.
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;
}
