main.c

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

char board[3][3];

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

void printBoard()
{
    printf("-------------\n");
    for (int i = 0; i < 3; i++)
    {
        printf("|");
        for (int j = 0; j < 3; j++)
        {
            printf(" %c |", board[i][j]);
        }
        printf("\n-------------\n");
    }
}

char win()
{
    for (int i = 0; i < 3; i++)
    {
        if (board[i][0] == board[i][1] && board[i][0] == board[i][2])
            return board[i][0];
        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[1][1] == board[2][0])
        return board[1][1];
    for (int i = 0; i < 3; i++)
    {
        for (int j = 0; j < 3; j++)
        {
            if (board[i][j] == ' ')
                return ' ';
        }
    }
    return 'T';
}

int tryMove(int row, int col, char playerSymbol)
{
    if (row >= 0 && row <= 2 && col >= 0 && col <= 2)
    {
        if (board[row][col] == ' ')
        {
            board[row][col] = playerSymbol;
            return 1;
        }
    }
    printf("Invalid move! Try again!\n");
    return 0;
}

void getHumanMove(char playerSymbol)
{
    printf("%c's turn!\n", playerSymbol);
    int row;
    int col;
    do
    {
        printf("Enter row (1-3): ");
        scanf("%d", &row);
        printf("Enter column (1-3): ");
        scanf("%d", &col);
    }
    while (!tryMove(row - 1, col - 1, playerSymbol));
    printBoard();
}

void getComputerMove(char playerSymbol)
{
    printf("%c's turn!\n", playerSymbol);
    int row, col;

    for (row = 0; row < 3; row++)
    {
        for (col = 0; col < 3; col++)
        {
            if (board[row][col] == ' ')
            {
                board[row][col] = playerSymbol;
                if (win() == playerSymbol)
                {
                    printf("Computer chose (%d, %d)\n", row + 1, col + 1);
                    printBoard();
                    return;
                }
                board[row][col] = ' ';
            }
        }
    }

    char opponentSymbol = (playerSymbol == 'X') ? 'O' : 'X';
    for (row = 0; row < 3; row++)
    {
        for (col = 0; col < 3; col++)
        {
            if (board[row][col] == ' ')
            {
                board[row][col] = opponentSymbol;
                if (win() == opponentSymbol)
                {
                    board[row][col] = playerSymbol;
                    printf("Computer chose (%d, %d)\n", row + 1, col + 1);
                    printBoard();
                    return;
                }
                board[row][col] = ' ';
            }
        }
    }

    if (board[1][1] == ' ')
    {
        board[1][1] = playerSymbol;
        printf("Computer chose (2, 2)\n");
        printBoard();
        return;
    }

    int corners[4][2] = {{0, 0}, {0, 2}, {2, 0}, {2, 2}};
    for (int i = 0; i < 4; i++)
    {
        row = corners[i][0];
        col = corners[i][1];
        if (board[row][col] == ' ')
        {
            board[row][col] = playerSymbol;
            printf("Computer chose (%d, %d)\n", row + 1, col + 1);
            printBoard();
            return;
        }
    }

    int edges[4][2] = {{0, 1}, {1, 0}, {1, 2}, {2, 1}};
    for (int i = 0; i < 4; i++)
    {
        row = edges[i][0];
        col = edges[i][1];
        if (board[row][col] == ' ')
        {
            board[row][col] = playerSymbol;
            printf("Computer chose (%d, %d)\n", row + 1, col + 1);
            printBoard();
            return;
        }
    }
}

int main(void)
{
    printf("Welcome to TicTacToe!\n");
    printf("Choose game mode:\n\t1 for human vs human\n\t2 for human vs "
           "computer\n\t3 for computer vs computer\n");
    char currentPlayer = 'X';
    int gameMode;
    scanf("%d", &gameMode);
    char humanSymbol = 'X';
    char computer1Symbol;
    char computer2Symbol;
    int isHumanVsHuman = 1;
    int isComputerVsComputer = 0;
    if (gameMode == 2)
    {
        printf("Do you want to play as X or O? ");
        scanf(" %c", &humanSymbol);
        humanSymbol = toupper(humanSymbol);
        computer1Symbol = (humanSymbol == 'X') ? 'O' : 'X';
        isHumanVsHuman = 0;
    }
    else if (gameMode == 3)
    {
        computer1Symbol = 'X';
        computer2Symbol = 'O';
        isHumanVsHuman = 0;
        isComputerVsComputer = 1;
    }
    initBoard();
    printBoard();
    do
    {
        if ((isHumanVsHuman || currentPlayer == humanSymbol) &&
                !isComputerVsComputer)
            getHumanMove(currentPlayer);
        else
            getComputerMove(currentPlayer);
        if (win() == 'T')
        {
            printf("It's a tie! ");
            return 0;
        }
        if (win() != ' ')
        {
            printf("%c won!", win());
            return 0;
        }
        currentPlayer = (currentPlayer == 'X') ? 'O' : 'X';
    }
    while (1);
    return 0;
}