Adding Stakes with ETH

Let's make the game more interesting by adding ETH stakes. Players will bet ETH, and the winner takes the pot!

The payable Keyword:

To receive ETH in a function, add the payable keyword.

function startGame(address _opponent) public payable { ... }

msg.value:

msg.value tells you how much ETH was sent with the function call.

It's measured in wei (1 ETH = 10^18 wei).

Storing the Stake:

Add a state variable: uint public stake;

In startGame, save the amount: stake = msg.value;

Resetting the Board:

When a new game starts, we need to clear the old board.

Use a for loop to reset all cells: for (uint i = 0; i < 9; i++) { board[i] = Cell.Empty; }

Update startGame to accept ETH stakes and reset the board.

Add ETH stakes to the game

Requirements:

Declares uint public stake

startGame is payable

Stores msg.value in stake

Clears board with for loop

Board reset is in startGame

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

contract TicTacToe {
    address public playerX;
    address public playerO;

    enum Cell { Empty, X, O }

    Cell[9] public board;

    bool public xTurn;
    bool public gameOver;
    address public winner;

    function startGame(address _opponent) public {
        playerX = msg.sender;
        playerO = _opponent;
        xTurn = true;
        gameOver = false;
        winner = address(0);
    }

    function makeMove(uint _position) public {
        require(!gameOver, "Game over");
        require(_position < 9, "Invalid position");
        require(board[_position] == Cell.Empty, "Cell already taken");
        require(xTurn ? msg.sender == playerX : msg.sender == playerO, "Not your turn");

        Cell piece = xTurn ? Cell.X : Cell.O;
        board[_position] = piece;

        if (checkWin()) {
            winner = msg.sender;
            gameOver = true;
        } else if (checkDraw()) {
            winner = address(0);
            gameOver = true;
        } else {
            xTurn = !xTurn;
        }
    }

    function checkWin() private view returns (bool) {
        // Check rows
        for (uint i = 0; i < 3; i++) {
            if (board[i*3] != Cell.Empty &&
                board[i*3] == board[i*3+1] &&
                board[i*3] == board[i*3+2]) {
                return true;
            }
        }

        // Check columns
        for (uint i = 0; i < 3; i++) {
            if (board[i] != Cell.Empty &&
                board[i] == board[i+3] &&
                board[i] == board[i+6]) {
                return true;
            }
        }

        // Check diagonals
        if (board[0] != Cell.Empty &&
            board[0] == board[4] &&
            board[0] == board[8]) {
            return true;
        }

        if (board[2] != Cell.Empty &&
            board[2] == board[4] &&
            board[2] == board[6]) {
            return true;
        }

        return false;
    }

    function checkDraw() private view returns (bool) {
        for (uint i = 0; i < 9; i++) {
            if (board[i] == Cell.Empty) {
                return false;
            }
        }
        return true;
    }
}