Bulls and Cows Classic

Bulls and Cows Classic app is the iOS realization of well-known logic puzzle game. Classic rules are quite simple. 
You have a code of 4 digits. All digits are unique and the 1st digit can't be a zero. Make your guesses by entering different digits. The game gives you hints with number of bulls and cows:
- if you have correct digit in correct place then you have a bull
- if you have correct digit but in wrong place then you have a cow

Good luck!