General Description of the game:
It's a two player game so the program takes the name of two players and assign O and X to the players.
Players enter their move turn by turn, into the box they choose.
Program needs to assure that no box is overwritten.
If the player tries to enter his/her move into the box that's already taken by the other player the the chance passes over to the other player.
Program needs to run till a player wins, want to quit the game or until there are no moves left.
After a player wins, program displays the message and will ask the player if he/she wants to play again.
Now let us analyze different elements of the game design in the program that we're going to make.