Tic-Tac-Toe Game Function To Check For Winner - c

Question

I've written the following code for a tic-tac-toe game on my own:
#include <stdio.h>
#include <math.h>
void instructions();
void printboard(char board[3][3]);
int wincheck(char board[3][3]);
int main(){
char tictac[3][3] = {{'-', '-', '-'}, {'-', '-', '-'}, {'-', '-', '-'}};
int player = 0;
int win = 0;
int player_choice = 0;
int row = 0;
int col = 0;
instructions();
for(int i=0; i<9 && win==0; i++){
printboard(tictac);
player = i%2 + 1;
do{
printf("\nPlayer #%d, enter your spot choice:\n", player);
scanf("%d", &player_choice);
if(player_choice == 1){
row = 0;
col = 0;
}
else if(player_choice == 2){
row = 0;
col = 1;
}
else if(player_choice == 3){
row = 0;
col = 2;
}
else if(player_choice == 4){
row = 1;
col = 0;
}
else if(player_choice == 5){
row = 1;
col = 1;
}
else if(player_choice == 6){
row = 1;
col = 2;
}
else if(player_choice == 7){
row = 2;
col = 0;
}
else if(player_choice == 8){
row = 2;
col = 1;
}
else if(player_choice == 9){
row = 2;
col = 2;
}
else{
printf("Not a valid choice, please choose again.");
}
}while(player_choice<0 || player_choice>9 || tictac[row][col]!='-');
if(player == 1){
tictac[row][col] = 'X';
}
else if(player == 2){
tictac[row][col] = 'O';
}
if(wincheck(tictac)!=0){
win = player;
}
}
printboard(tictac);
if(!win){
printf("\n\nTHE GAME IS A DRAW!\n");
}
else{
printf("\n\nCONGRATULAIONS PLAYER #%d, YOU WON!\n", win);
}
}
void instructions(){
printf("\n\t\t\t WELCOME TO TIC TAC TOE!\n");
printf("\nGame Rules:\n");
printf("\nThe program will ask the player to enter which spot they would like to place their X or O.\nPlease use spot numbers as shown below:\n\n");
printf("\t\t\t\t 1 | 2 | 3 \n");
printf("\t\t\t\t---+---+---\n");
printf("\t\t\t\t 4 | 5 | 6 \n");
printf("\t\t\t\t---+---+---\n");
printf("\t\t\t\t 7 | 8 | 9 \n");
printf("\n\t------------------------LET'S BEGIN!------------------------\n\n\n");
}
void printboard(char board[3][3]){
printf("\t\t\t\t %c | %c | %c \n", board[0][0], board[0][1], board[0][2]);
printf("\t\t\t\t---+---+---\n");
printf("\t\t\t\t %c | %c | %c \n", board[1][0], board[1][1], board[1][2]);
printf("\t\t\t\t---+---+---\n");
printf("\t\t\t\t %c | %c | %c \n", board[2][0], board[2][1], board[2][2]);
}
int wincheck(char board[3][3]){
if((board[0][0]==board[0][1] && board[0][0]==board[0][2]) || (board[1][0]==board[1][1] && board[1][0]==board[1][2]) || (board[2][0]==board[2][1] && board[2][0]==board[2][2])){
return 1;/*Checks to see if player has won across any of the rows.*/
}
else if((board[0][0]==board[1][0] && board[0][0]==board[2][0]) || (board[0][1]==board[1][1] && board[0][1]==board[2][1]) || (board[0][2]==board[1][2] && board[0][2]==board[2][2])){
return 1;/*Checks to see if player has won down any columns.*/
}
else if((board[0][0]==board[1][1] && board[0][0]==board[2][2]) || (board[0][2]==board[1][1] && board[0][2]==board[2][0])){
return 1;/*Checks to see if player has won in a diagonal.*/
}
else{
return 0;
}
}
I'm running into an issue when trying to play the game though. After the first player chooses a "play spot" it thinks they have won already. Because of this I believe the issue is most likely due to an error in the wincheck function but I can't quite figure out what exactly is causing the issue. I'm a beginner programmer, so I apologize if this is kind of a dumb question. I really appreciate any help you can offer!

Answer 1

The problem is indeed with your wincheck function. It rightly checks that the three candidate cells are equal but does not check that those cells have been populated. That means the game will be detected as won even before a move is made (since all cells are set to -, a simple equality check will pass).
It's therefore not enough to do just the equality check, you also have to ensure that at least one of those cells has been set to a real player.
You can also make your code a bit more readable with a little refactoring, something like:
// Returns the actual winner, or '-' if none. Needs x/y start cell
// and x/y deltas (direction, basically).
int checkOneWinPossibility(char board[3][3], int x, int y, int xd, int yd) {
// Check all no-winner scenarios, return winner only if they all fail.
if (board[x][y] == '-') return '-';
if (board[x][y] != board[x+xd][y+yd]) return '-';
if (board[x][y] != board[x+xd*2][y+yd*2]) return '-';
return board[x][y];
}
int checkAllWinPossibilities(char board[3][3]){
int winner;
// Horizontals.
if ((winner = checkOneWinner(board, 0, 0, 0, 1)) != '-') return winner;
if ((winner = checkOneWinner(board, 1, 0, 0, 1)) != '-') return winner;
if ((winner = checkOneWinner(board, 2, 0, 0, 1)) != '-') return winner;
// Verticals.
if ((winner = checkOneWinner(board, 0, 0, 1, 0)) != '-') return winner;
if ((winner = checkOneWinner(board, 0, 1, 1, 0)) != '-') return winner;
if ((winner = checkOneWinner(board, 0, 2, 1, 0)) != '-') return winner;
// Diagonals.
if ((winner = checkOneWinner(board, 0, 0, 1, 1)) != '-') return winner;
if ((winner = checkOneWinner(board, 2, 0, -1, 1)) != '-') return winner;
return '-';
}
That last diagonal check could be combined with the return statement just by doing:
return checkOneWinner(board, 2, 0, -1, 1);
but I prefer (being slightly OCD) to leave it as is for consistency :-)
They also both return the actual winner rather than just an indication that there is a winner. You may not need that information since it will obviously be the last player that moved, but there's no probably no substantial harm in returning the extra information.