Tic-tac-toe

Tic-tac-toe (Xs and Os) is a game for two players, who take turns marking the spaces in a 3×3 grid. The player who succeeds in placing three of their marks in a horizontal, vertical, or diagonal row wins the game.
Rules:
1. The game is played on a grid that's 3 squares by 3 squares.
2. You are X, your friend (or the computer in this case) is O. Players take turns putting their marks in empty squares.
3. The first player to get 3 of her marks in a row (up, down, across, or diagonally) is the winner.
4. When all 9 squares are full, the game is over. If no player has 3 marks in a row, the game ends in a tie.