main.c

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

char board[3][3];
const char PLAYER = 'X';
const char COMPUTER = 'O';

void resetBoard();
void printBoard();
int checkFreeSpaces();
void playerMove();
void computerMove();
char checkWinner();
void printWinner(char);


int main() {
    char winner;
    char response;

    do{
        winner = ' ';
        response = ' ';
        resetBoard();
        while(winner == ' ' && checkFreeSpaces() != 0) {
            printBoard();

            playerMove();
            winner = checkWinner();
            if (winner != ' ' || checkFreeSpaces() == 0) {
                break;
            }

            computerMove();
            winner = checkWinner();
            if (winner != ' ' || checkFreeSpaces() == 0) {
                break;
            }
        }

        printBoard();
        printWinner(winner);

        printf("\nWould you like to play again? (Y/N): ");
        scanf("%c");
        scanf("%c", &response);
        response = toupper(response);
    } while (response == 'Y');

    printf("Thanks for playing!");

    return 0;
}

void resetBoard(){
    for(int i =0; i < 3; i++){
        for(int j =0; j< 3; j++){
            board[i][j] = ' ';
        }
    }
}

void printBoard(){
    printf(" %c | %c | %c ", board[0][0], board[0][1], board[0][2]);
    printf("\n---|---|---\n");
    printf(" %c | %c | %c ", board[1][0], board[1][1], board[1][2]);
    printf("\n---|---|---\n");
    printf(" %c | %c | %c ", board[2][0], board[2][1], board[2][2]);
    printf("\n");
}

int checkFreeSpaces(){
    int freeSpaces = 9;
    for(int i = 0; i < 3; i++){
        for(int j = 0; j< 3; j++){
            if(board[i][j] != ' '){
                freeSpaces--;
            }
        }
    }
    return freeSpaces;
}

void playerMove(){
    int x;
    int y;

    do {
        printf("Enter row #(1-3): ");
        scanf("%d", &x);
        x--;

        printf("Enter colum #(1-3): ");
        scanf("%d", &y);
        y--;

        if(board[x][y] != ' '){
            printf("Invalid move!\n");
        } else {
            board[x][y] = PLAYER;
            break;
        }
    } while (board[x][y] != ' ');
}

void computerMove(){
    srand(time(0));
    int x;
    int y;

    if(checkFreeSpaces() > 0 ){
        do {
            x = rand() % 3;
            y = rand() % 3;
        } while (board[x][y] != ' ');

        board[x][y] = COMPUTER;
    } else {
        printWinner(' ');
    }
}

char checkWinner(){
    for(int i =0; i<3; i++){
        if(board[i][0] == board[i][1] && board[i][0] == board[i][2]){
            return board[i][0];
        }
    }

    for(int i =0; i<3; i++){
        if(board[0][i] == board[1][i] && board[0][i] == board[2][i]){
            return board[0][i];
        }
    }

    if(board[0][0] == board[1][1] && board[0][0] == board[2][2]){
        return board[0][0];
    }

    if(board[0][2] == board[1][1] && board[0][0] == board[2][0]){
        return board[0][0];
    }

    return ' ';


}

void printWinner(char winner){
    if( winner == PLAYER){
        printf("YOU WIN");
    } else if ( winner == COMPUTER) {
        printf("YOU LOSE");
    } else {
        printf("ITS A TIE");
    }
}