Introduction

Tic-Tac-Toe is a classic two-player game where players take turns marking a grid of 3×3 with either an ‘X’ or an ‘O’. The objective of the game is to be the first to form a horizontal, vertical, or diagonal line of three matching symbols.

In this program, we will create a simple text-based Tic-Tac-Toe game in the C programming language. Players will input their moves by specifying the row and column where they want to place their symbol. The program will check for a winner after each move and declare the winner once one player achieves the objective or if the game ends in a draw.

Objective

The objective of this program is to provide a clear example of how a simple Tic-Tac-Toe game can be implemented in C. This program will demonstrate how to:

• Create a game board using a 2D array.
• Implement game logic to allow two players to take turns.
• Check for a winner or a draw after every move.

Code

#include 

char board[3][3] = {{'1', '2', '3'}, {'4', '5', '6'}, {'7', '8', '9'}};
int player = 1;  // Player 1 starts
int choice;
int row, column;
char mark;

void printBoard() {
    printf("\n\n");
    printf(" Tic-Tac-Toe \n");
    printf(" Player 1 (X) - Player 2 (O) \n\n");
    printf("  %c | %c | %c \n", board[0][0], board[0][1], board[0][2]);
    printf(" ---|---|--- \n");
    printf("  %c | %c | %c \n", board[1][0], board[1][1], board[1][2]);
    printf(" ---|---|--- \n");
    printf("  %c | %c | %c \n", board[2][0], board[2][1], board[2][2]);
    printf("\n\n");
}

int checkWin() {
    // Check rows and columns for a winner
    for (int i = 0; i < 3; i++) {
        if (board[i][0] == board[i][1] && board[i][1] == board[i][2])
            return 1;
        if (board[0][i] == board[1][i] && board[1][i] == board[2][i])
            return 1;
    }
    // Check diagonals
    if (board[0][0] == board[1][1] && board[1][1] == board[2][2])
        return 1;
    if (board[0][2] == board[1][1] && board[1][1] == board[2][0])
        return 1;
    return 0;
}

int checkDraw() {
    for (int i = 0; i < 3; i++) {
        for (int j = 0; j < 3; j++) {
            if (board[i][j] != 'X' && board[i][j] != 'O') {
                return 0;
            }
        }
    }
    return 1;
}

int main() {
    printf("Welcome to Tic-Tac-Toe Game!\n");
    printBoard();

    while (1) {
        // Alternate between player 1 and player 2
        player = (player % 2) ? 1 : 2;

        // Get player input
        printf("Player %d, enter a number (1-9): ", player);
        scanf("%d", &choice);

        // Determine row and column
        row = (choice - 1) / 3;
        column = (choice - 1) % 3;

        // Check if the cell is already filled
        if (board[row][column] == 'X' || board[row][column] == 'O') {
            printf("This cell is already filled, please try again.\n");
            continue;
        }

        // Mark the board
        mark = (player == 1) ? 'X' : 'O';
        board[row][column] = mark;
        
        // Print the updated board
        printBoard();

        // Check if there is a winner
        if (checkWin()) {
            printf("Player %d wins!\n", player);
            break;
        }

        // Check for a draw
        if (checkDraw()) {
            printf("The game is a draw!\n");
            break;
        }

        // Switch players
        player++;
    }

    return 0;
}

Explanation of the Program Structure

This C program is designed to implement a simple Tic-Tac-Toe game for two players. Here’s a breakdown of the program’s structure:

• Board Representation: The game board is represented as a 2D array `board[3][3]`, where each element corresponds to a cell in the grid.
• Player Turns: The variable `player` tracks the current player (either 1 or 2). Player 1 uses ‘X’ and Player 2 uses ‘O’.
• Input Handling: Players input their move by entering a number between 1 and 9, which corresponds to a position on the board.
• Game Logic: After each move, the program checks for a winner using the `checkWin` function, and checks for a draw using the `checkDraw` function. If a player wins or the game ends in a draw, the game announces the result and exits.

How to Run the Program

1. Copy the C code provided above into a text file and save it with a `.c` extension (e.g., `tictactoe.c`).
2. Compile the code using a C compiler, for example, using GCC: gcc tictactoe.c -o tictactoe.
3. Run the compiled program by typing: ./tictactoe in the terminal.
4. Follow the on-screen instructions to play the game.