I'd use an Array. If its empty that means position 1 is free, and you add to it.
Next time you'll count it and get 1, so you add the next one to that index.
If you're super new and that sounds confusing, go through the Arraymaker tutorials before doing anything.
However, Mutajon's suggestion is simpler and would also work, but you wouldn't be able to go back and get those values by their corresponding slots later on