Tic Tac Toe C program, win conditions not working

Question

This is a program that allows you to play a 5x5 tic tac toe game with a computer. I am going to implement smart steps for the computer, but first I need to fix the check for winning. If you win with a column or diagonal, it works, but winning with a row only works on line 2 + 3, and not on line 4 or 5. Can someone tell me why? I use exclusively C.

#include <stdio.h>
#include <stdlib.h>

char matrix[5][5];  /* 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("Computer won.\n");
  disp_matrix(); /* show final positions */

  return 0;
}

/* Initialize the matrix. */
void init_matrix(void)
{
  int i, j;

  for(i=0; i<5; i++)
    for(j=0; j<5; j++) matrix[i][j] =  ' ';
}

/* Get a player 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<5; i++){
    for(j=0; j<5; j++)
      if(matrix[i][j]==' ') break;
    if(matrix[i][j]==' ') break;
  }

  if(i*j==25)  {
    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<5; t++) {
    printf(" %c | %c | %c | %c | %c ",matrix[t][0], matrix[t][1], matrix [t][2], matrix[t][3], matrix[t][4]);
    if(t!=4) printf("\n---|---|---|---|---\n");
  }
  printf("\n");
}

/* See if there is a winner. */
char check(void)
{
  int i;

  for(i=0; i<5; i++)  /* check rows */
    if(matrix[i][0]==matrix[i][1] &&
       matrix[i][0]==matrix[i][2] &&
       matrix[i][0]==matrix[i][3] &&
       matrix[i][0]==matrix[i][4]) return matrix[i][0];

  for(i=0; i<5; i++)  /* check columns */
    if(matrix[0][i]==matrix[1][i] &&
       matrix[0][i]==matrix[2][i] &&
       matrix[0][i]==matrix[3][i] &&
       matrix[0][i]==matrix[4][i]) return matrix[0][i];

  /* test diagonals */
  if(matrix[0][0]==matrix[1][1] &&
     matrix[1][1]==matrix[2][2] &&
     matrix[2][2]==matrix[3][3] &&
     matrix[3][3]==matrix[4][4])
       return matrix[0][0];

  if(matrix[0][4]==matrix[1][3] &&
     matrix[1][3]==matrix[2][2] &&
     matrix[2][2]==matrix[3][1] &&
     matrix[3][1]==matrix[4][0])
       return matrix[0][4];

  return ' ';
}

Answer 1

This does not work, because it will be returned “prematurely” to completely empty lines. Therefore, you need to perform an additional check:

if(matrix[i][0]==matrix[i][1] &&
   matrix[i][0]==matrix[i][2] &&
   matrix[i][0]==matrix[i][3] &&
   matrix[i][0]==matrix[i][4] &&
   matrix[i][0] != ' ')
      return matrix[i][0];

This also applies to other checks.