A pencil (or pen) and a piece of paper for each player.
To be the first player to successfully decode your opponent's secret number.
Each player writes a four-digit number on a piece of paper, taking care to ensure that the other player does not see the number. The digits must all be different. (For example, 4729 would be legal, but 4724 would not be legal.)
Determine which player will guess first.
In turn, players try to guess their opponent's number. The opponent responds by announcing the number of matches.
A digit which is in the number but not announced in the correct position is a "cow." A digit which is in the number and is announced in the correct position is a "bull."
EXAMPLE: Andre's secret number is 8045. Beth guesses 0865. There are two cows (0 and 8) and one bull (5). Andre says, "There are two cows and one bull." Andre does not reveal which digits are the cows and which one is the bull.
The first player to reveal his opponent's secret number wins.
EXCEPTION: If the player who guesses first is also the first to reveal his opponent's secret number, the second player gets one final guess. If this guess is successful, the game ends in a tie. (This ensures that both players have the same number of turns.)
The game can be made more challenging by using five-digit or six-digit secret numbers.
Bulls and Cows is also known as Cows and Bulls, Pigs and Bulls, and Bulls and Cleots.