Complex Conditions

Right now, anyone can make a move. We need to ensure only the correct player can move on their turn.

Combining Concepts:

We can use the ternary operator inside a require statement to check different conditions.

The Logic:

• If it's X's turn (xTurn is true), require that msg.sender == playerX

• If it's O's turn (xTurn is false), require that msg.sender == playerO

Using Ternary in Require:

require(xTurn ? msg.sender == playerX : msg.sender == playerO, "Not your turn");

This reads as: "Require that if xTurn is true, the sender is playerX, otherwise the sender is playerO."

Add this validation to makeMove after the other require statements to ensure players can only move on their turn.

Validate correct player's turn

Requirements:

Has turn validation require

Uses ternary operator in require

Checks playerX when xTurn is true

Checks playerO when xTurn is false

Inside makeMove function

// 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;

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

    function makeMove(uint _position) public {
        require(_position < 9, "Invalid position");
        require(board[_position] == Cell.Empty, "Cell already taken");

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

        xTurn = !xTurn;
    }
}