Author: William Gerbert

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.


1   program CardTest;
2   
3   uses
4     Dialogs,
5     SysUtils;
6   
7   {$R *.RES}
8   
9   const
10    CardType: array[0..4] of string = ('Invalid', 'Amex', 'Visa', 'Mastercard',
11      'Discover');
12  
13  function Vc(C: string): Integer;
14  var
15    Card: string[21];
16    VCard: array[0..21] of Byte absolute Card;
17    XCard: Integer;
18    Cstr: string[21];
19    y,
20      x: Integer;
21  begin
22    Cstr := '';
23    FillChar(VCard, 22, #0);
24    Card := C;
25    for x := 1 to 20 do
26      if (VCard[x] in [48..57]) then
27        Cstr := Cstr + Chr(VCard[x]);
28    Card := '';
29    Card := Cstr;
30    XCard := 0;
31    if not odd(Length(Card)) then
32      for x := (Length(Card) - 1) downto 1 do
33      begin
34        if odd(x) then
35          y := ((VCard[x] - 48) * 2)
36        else
37          y := (VCard[x] - 48);
38        if (y >= 10) then
39          y := ((y - 10) + 1);
40        XCard := (XCard + y)
41      end
42    else
43      for x := (Length(Card) - 1) downto 1 do
44      begin
45        if odd(x) then
46          y := (VCard[x] - 48)
47        else
48          y := ((VCard[x] - 48) * 2);
49        if (y >= 10) then
50          y := ((y - 10) + 1);
51        XCard := (XCard + y)
52      end;
53    x := (10 - (XCard mod 10));
54    if (x = 10) then
55      x := 0;
56    if (x = (VCard[Length(Card)] - 48)) then
57      Vc := Ord(Cstr[1]) - Ord('2')
58    else
59      Vc := 0
60  end;
61  
62  begin
63    ShowMessage(CardType[Vc('4479750100222862')]);
64  end.