CSci 3102  Winter 1994  Extension
Lab 4
Due: 28 Feb.

Write a program that will tic-tac-toe between two players.
The board is the traditional 3x3.
The computer is not a player.

The players will be prompted for their moves, in turn.
Input must be checked to be sure it is valid and that the
position has not already been played.

A 2-dimensional array must be used as the data structure
that represents the board.  Pass it to and from procedures/
functions.  Use a Type definition for boards.