Tic Tac Toe

a game in which two players seek in alternate turns to complete a row, a column, or a diagonal with either three O's or three X's drawn in the spaces of a grid of nine squares; noughts and crosses
The game is played on a grid that's 3 squares by 3 squares.
You are X, your friend is O. Players take turns putting their marks in empty squares.
The first player to get 3 of her marks in a row (up, down, across, or diagonally) is the winner.
When all 9 squares are full, the game is over.