Write a program play tic-tac-toe against the user. First, query who should go first:
Do you want to go first (y/n)?
Give each box a coordinate, e.g., A3 or C1:
1 2 3 | | A | | ---+---+--- B | | ---+---+--- C | | | |
Now, place either an X or an O as appropriate. If someone wins, indicate so; otherwise indicate a draw:
1 2 3 | | A X | O | X ---+---+--- B O | O | X ---+---+--- C X | X | O | | DRAW! Do you want to play again (y/n)?
You, as the programmer of the computer, should never lose against the human player.