The computer guesses a four-digit number, the numbers in it do not repeat, 0 can stand in the first place. The player can make 10 moves to find this number. In response to every move the computer shows the number of guessed digits, standing in their places (the number of bulls) and the number of guessed digits, not standing in their places (number of cows).
Example:
The computer conceived 0834. The player entered 8134. The computer responded: 2 bulls (digits 3 and 4) and 1 cow (digit 8).