Cows and Bulls - Guess Numbers

Cows and Bulls is an old code-breaking mind game.

How To Play:
The objective of this game is to break the code getting clues for each guess.
Application will generate random number, which you will have to guess. The digits of the number will be all different.

Clues:
If the matching digits are in their right positions, they are "bulls", if in different positions, they are "cows". Example:
- Secret number: 4271
- Opponent's try: 1234
- Answer: 1 bull and 2 cows. (The bull is "2", the cows are "4" and "1".)