Nested Loops

Now we need to detect when a player has won by getting three in a row.

Board Layout:

Our board is stored as a flat array with 9 positions:

[0, 1, 2, 3, 4, 5, 6, 7, 8]

This represents a 3x3 grid:

Row 0: positions 0, 1, 2
Row 1: positions 3, 4, 5
Row 2: positions 6, 7, 8

The && Operator:

&& means "and". All conditions must be true.

a == b && b == c means "a equals b AND b equals c"

Checking Rows:

For row i, the three positions are: i*3, i*3+1, i*3+2

Row 0: 0*3 = 0, 0*3+1 = 1, 0*3+2 = 2
Row 1: 1*3 = 3, 1*3+1 = 4, 1*3+2 = 5
Row 2: 2*3 = 6, 2*3+1 = 7, 2*3+2 = 8

Create a checkWin function that loops through the 3 rows and checks if all three cells match and aren't Empty.

Create checkWin function for rows

Requirements:

Declares function checkWin

Function is private view

Returns bool

Has for loop checking 3 rows

Checks cell is not Empty

Uses && operator

Checks all three cells in row match

Returns true if match found

Returns false at end

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

    // Add checkWin function here
}