Credit Card Validation

Problem/Question/Abstract:

Credit Card Validation

Answer:

Are you in need to validate a credit card? The following routine does some basic checking and returns the type of the credit card as a number - or use the const array to get the type of credit card by name. (E.g. 'Mastercard').

This code does not check that the credit card is actually valid, that it is good for a purchase or whether it belongs to a certain person. To accept any kind of orders, you need to do an address verification, combined with checking the expiration date.

The routine is still handy as an input validator on forms. You may download it here.


program CardTest;

uses
  Dialogs,
  SysUtils;

{$R *.RES}

const
  CardType: array[0..4] of string = ('Invalid', 'Amex', 'Visa', 'Mastercard',
    'Discover');

function Vc(C: string): Integer;
var
  Card: string[21];
  VCard: array[0..21] of Byte absolute Card;
  XCard: Integer;
  Cstr: string[21];
  y,
    x: Integer;
begin
  Cstr := '';
  FillChar(VCard, 22, #0);
  Card := C;
  for x := 1 to 20 do
    if (VCard[x] in [48..57]) then
      Cstr := Cstr + Chr(VCard[x]);
  Card := '';
  Card := Cstr;
  XCard := 0;
  if not odd(Length(Card)) then
    for x := (Length(Card) - 1) downto 1 do
    begin
      if odd(x) then
        y := ((VCard[x] - 48) * 2)
      else
        y := (VCard[x] - 48);
      if (y >= 10) then
        y := ((y - 10) + 1);
      XCard := (XCard + y)
    end
  else
    for x := (Length(Card) - 1) downto 1 do
    begin
      if odd(x) then
        y := (VCard[x] - 48)
      else
        y := ((VCard[x] - 48) * 2);
      if (y >= 10) then
        y := ((y - 10) + 1);
      XCard := (XCard + y)
    end;
  x := (10 - (XCard mod 10));
  if (x = 10) then
    x := 0;
  if (x = (VCard[Length(Card)] - 48)) then
    Vc := Ord(Cstr[1]) - Ord('2')
  else
    Vc := 0
end;

begin
  ShowMessage(CardType[Vc('4479750100222862')]);
end.