OK
Rules:
1. Choose only 4 unique digits in any combination (0 can't be used).
2. Only positive integers are allowed.
3. For each digit that is in it's place, you get a bull,
	and for each digit that is not in it's place, you get a cow.
4. The game is won when your number matches the number I chose.

Press [esc] to quit the game.

OK

Enter your number:  2468
Bulls: 0 Cows: 2

Enter your number:  2448
The number can only have unique digits.

Enter your number:  1357
Bulls: 0 Cows: 1