With arrays you can do marvelous things, such as load a dozen things into a single variable. As well manipulate them to work with loops. However, in this case you should not be using regular arrays because this can cause severe lag issues. What I recommend is that you work with Flexible Arrays instead. What I mean by flexible is that you can easily push new values into the array.
var CARD : flexible array 1..0 of int
When you push new values you increase the 0 each time representing the cards used. Still stuck? Well whenever you push a new value remember, the value is stored. You can use this to your advantage as to checking for duplicates or cards that are used more then once. Anyways I left a few links below good luck.
Normal arrays (get the concept)
http://compsci.ca/holtsoft/doc/array.html
Flexible arrays (Alternative)
http://compsci.ca/holtsoft/doc/flexible.html
Extra help (looping)
http://compsci.ca/holtsoft/doc/for.html