A Tic-Tac-Toe Game Example in C,C++

The longer example that follows illustrates many of the ways that you can manipulate
arrays with C/C++. This section develops a simple tic-tac-toe program.
Two-dimensional arrays are commonly used to simulate board game matrices.
The computer plays a very simple game. When it is the computer's turn, it uses
get_computer_move() to scan the matrix, looking for an unoccupied cell. When it finds
one, it puts an O there. If it cannot find an empty location, it reports a draw game and
exits. The get_player_move() function asks you where you want to place an X. The
upper-left corner is location 1,1; the lower-right corner is 3,3.
The matrix array is initialized to contain spaces. Each move made by the player or
the computer changes a space into either an X or an O. This makes it easy to display the
matrix on the screen.
Each time a move has been made, the program calls the check() function. This
function returns a space if there is no winner yet, an X if you have won, or an O if the
computer has won. It scans the rows, the columns, and then the diagonals, looking for
one that contains either all X's or all O's.
The disp_matrix() function displays the current state of the game. Notice how
initializing the matrix with spaces simplified this function.
The routines in this example all access the matrix array differently. Study them to
make sure that you understand each array operation.
/* A simple Tic Tac Toe game. */
#include <stdio.h>
#include <stdlib.h>
char matrix[3][3]; /* the tic tac toe matrix */
char check(void);
void init_matrix(void);
void get_player_move(void);
void get_computer_move(void);
void disp_matrix(void);
int main(void)
{
char done;
printf("This is the game of Tic Tac Toe.\n");
printf("You will be playing against the computer.\n");
done = ' ';

init_matrix();
do{
disp_matrix();
get_player_move();
done = check(); /* see if winner */
if(done!= ' ') break; /* winner!*/
get_computer_move();
done = check(); /* see if winner */
} while(done== ' ');
if(done=='X') printf("You won!\n");
else printf("I won!!!!\n");
disp_matrix(); /* show final positions */
return 0;
}
/* Initialize the matrix. */
void init_matrix(void)
{
int i, j;
for(i=0; i<3; i++)
for(j=0; j<3; j++) matrix[i][j] = ' ';
}
/* Get a player's move. */
void get_player_move(void)
{
int x, y;
printf("Enter X,Y coordinates for your move: ");
scanf("%d%*c%d", &x, &y);
x--; y--;
if(matrix[x][y]!= ' '){
printf("Invalid move, try again.\n");
get_player_move();
}
else matrix[x][y] = 'X';
}

/* Get a move from the computer. */
void get_computer_move(void)
{
int i, j;
for(i=0; i<3; i++){
for(j=0; j<3; j++)
if(matrix[i][j]==' ') break;
if(matrix[i][j]==' ') break;
}
if(i*j==9) {
printf("draw\n");
exit(0);
}
else
matrix[i][j] = 'O';
}
/* Display the matrix on the screen. */
void disp_matrix(void)
{
int t;
for(t=0; t<3; t++) {
printf(" %c | %c | %c ",matrix[t][0],
matrix[t][1], matrix [t][2]);
if(t!=2) printf("\n---|---|---\n");
}
printf("\n");
}
/* See if there is a winner. */
char check(void)
{
int i;
for(i=0; i<3; i++) /* check rows */
if(matrix[i][0]==matrix[i][1] &&
matrix[i][0]==matrix[i][2]) return matrix[i][0];
for(i=0; i<3; i++) /* check columns */
if(matrix[0][i]==matrix[1][i] &&

/* test diagonals */
if(matrix[0][0]==matrix[1][1] &&
matrix[1][1]==matrix[2][2])
return matrix[0][0];
if(matrix[0][2]==matrix[1][1] &&
matrix[1][1]==matrix[2][0])
return matrix[0][2];
return ' ';
}