Bulls and Cows is a classic puzzle game.

The rules of the game are simple:
The computer guesses four numbers, for example 1234 (the numbers cannot be repeated).
You have to try to guess that number.
After each attempt, the computer tells you how many numbers you guessed, and how many of them are in the right places.
If the assigned number is 1234 and you tried 1243, it means that you guessed two numbers in the right places (1 and 2) and two numbers in the wrong places (4 and 3).
The game continues until you have identified all the numbers in the correct places.

Good luck!