Instructions:
1. Players must select their mark before the game starts (either X or O) and must
play the entire game using the same mark.
2. Players must take turns, making only one mark with each turn.
3. Marks can only be placed in empty squares, and once it is placed, it is
permanent.
4. The winner is the first player to get three of their marks in a straight line
(the line can be positioned diagonally, vertically, or horizontally).
5. The game is over when all nine squares are filled with marks, even if none of the
players have a straight line of three marks.
6. If neither player has a straight line of three marks, it is considered a tie.
