Thinking--Guess Digits game

Play process:
1. Pressure "SetDigits" for system to randomly set 4 different digits.
2. Enter digits to guess and click "Guess" to get the reply ?A?B.
3. A means number of correct digit @ correct location.
4. B means number of correct digits @ incorrect location.
5 for example if 7290 was setted and you guess 6207, the reply will be
1A(2 @ correct location), 2B(7, 0 @ incorrect location).
6. Repeat 2~5 until the answer is 4A to finish the game.
7. If "Abort" clicked, the digits set will be appeared.