Helper Functions

Now let's turn our isBoardFull function into a proper helper function.

Private Functions:

Functions marked private can only be called from inside the contract. They're perfect for helper functions.

View Functions:

Functions that only read data (don't modify state) should be marked view. This tells Solidity the function won't change anything.

Return Values:

Use returns (type) to specify what a function gives back.

Example:

function isWinner() private view returns (bool) { ... }

Rename isBoardFull to checkDraw and change it from public view to private view. This makes it a helper function only for internal use.

Create private checkDraw function

Requirements:

Renamed to checkDraw

Function is private

Function is view

Returns bool

Has for loop logic

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

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

        xTurn = !xTurn;
    }

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