Declaring winner in tic tac toe board - c

Question

I wrote a code for a tic tac toe problem where you input the numbers into the array and the board will be printed out. There is also a function that declares the winner, but doesn't seem to be working, the function is supposed to declares the winner for any size of a tic tac toe board (right now it is 5x5).
I did a double for loop with it checking if the character is the same in the array as next to it so it moves along the rows, there's another for columns, one diagonal and the other. For some reason it isn't showing any winners, no winners always comes up. Any help is appreciated.
#include <stdio.h>
#define TRUE 1
#define FALSE 0
#define SIZE 3
#define NONE -1
#define NOUGHTS 0
#define CROSSES 1
#define EMPTY 2
void scanBoard(int board[SIZE][SIZE]);
void printBoard(int board[SIZE][SIZE]);
int getWinner(int board[SIZE][SIZE]);
int main( void ){
int board[SIZE][SIZE];
int winner;
printf("Please enter the board:\n");
scanBoard( board );
printf("Here is the board:\n");
printBoard( board );
printf("The winner is: ");
winner = getWinner(board);
if(winner == CROSSES){
printf("Crosses");
}
else if(winner == NOUGHTS){
printf("Noughts");
}
else{
printf("No one");
}
return 0;
}
void scanBoard(int board[SIZE][SIZE]){
int i;
int j;
for(i=0; i<SIZE; i++){
for(j=0; j<SIZE; j++){
scanf("%d", &board[i][j]);
}
}
}
void printBoard(int board[SIZE][SIZE]){
int i;
int j;
for(i=0; i<SIZE; i++){
for(j=0; j<SIZE; j++){
if(board[i][j] == EMPTY){
printf(". ");
}
else if(board[i][j] == CROSSES){
printf("X ");
}
else if(board[i][j] == NOUGHTS){
printf("O ");
}
}
printf("\n");
}
}
int getWinner(int board[SIZE][SIZE]){
int i;
int j;
int check;
int winner;
for(i=0; i<SIZE; i++){
for(j=0; j<SIZE-1 && check == TRUE; j++){
if(board[i][j] != board[i][j+1]){
check = FALSE;
}
}
if(check == TRUE && j == SIZE-1){
winner=board[i][0];
}
}
for(j=0; j<SIZE; j++){
for(i=0; i<SIZE-1 && check == TRUE; i++){
if(board[i][j] != board[i+1][j]){
check = FALSE;
}
}
if(check == TRUE && i == SIZE-1){
winner=board[0][j];
}
}
for(i=0; i<SIZE-1 && check == TRUE; i++){
if(board[i][i] != board[i+1][i+1]){
check = FALSE;
}
if(check == TRUE && i == SIZE-1){
winner=(board[i][i]);
}
}
for(i=SIZE; i>0 && check == TRUE; i--){
if( board[i][i] != board[i-1][i-1])
check = FALSE;
}
if(check == TRUE && i == SIZE-1){
winner=(board[i][i]);
}
return winner;
}

Answer 1

I did not go completely through your checking logic but here directly in getWinner, you are trigerring undefined behaviour:
for(j=0; j<SIZE-1 && check == TRUE; j++){
by reading check variable which has not been initialized (result of this is that any kind of behaviour can happen). So you may want to initialize it to default value first.
There are some implementationos of that game around, I suggest you look at some similar implementation and compare against your winner checking logic for example.

Answer 2

As Giorgi pointed out, you have to initialize check before you start testing its value. You also need to initialize winner to EMPTY at the start of the getWinner() function, otherwise if there is no winner, your function will return some unpredictable junk value and your main() function will probably print out the wrong result.
int getWinner(int board[SIZE][SIZE]){
int i;
int j;
int check;
int winner=EMPTY /* <<< */;
for(i=0; i<SIZE; i++){
for(j=0, check=TRUE /* <<< */; j<SIZE-1 && check == TRUE; j++){
if(board[i][j] != board[i][j+1]){
check = FALSE;
}
}
if(check == TRUE && j == SIZE-1){
winner=board[i][0];
}
}
for(j=0; j<SIZE; j++){
for(i=0, check=TRUE /* <<< */; i<SIZE-1 && check == TRUE; i++){
if(board[i][j] != board[i+1][j]){
/** etc... **/
(Note: There's also no need to continue checking once you've found a winner, so perhaps instead of winner=board[i][j]; you could just return board[i][j];. Not a big deal, though.)
You are also checking one of the diagonals twice (in two different directions). The other diagonal isn't being checked at all.