Java Tic Tac Toe win-condition

Question

I am currently working on an assignment, which is to create a Tic Tac Toe game. I got to the point where players can place their marks on the board, draw it and switch turns after. However, my check if a win-condition exists only seems to evaluate to true when a player places his mark in the top left (1st) field.

I've been trying to work with this answer to get it right, but no luck so far and I don't want to just copy that answer, but know where my coding is flawed. The debugger isn't giving me much. I suspect it has something to do with the way playerTurn() is set up. What am I missing? Any help would be appreciated.

Here's my code:

import java.util.Scanner;

public class tictactoe {

private static char[][] board;
private char currentPlayer = 'X';

public static void main(String[] args) {
    board = new char [3][3];
    tictactoe game = new tictactoe();

    game.welcomeAndInstruct();
    game.boardInit();
    game.playerTurn();

}

public void playerTurn() {
    do {
        Scanner input = new Scanner(System.in);
        System.out.print("Player " + currentPlayer + "'s turn: ");
        int move = input.nextInt();
        if (move == 1) {
            placeMark(0, 0);
            drawBoard();
        } else if (move == 2) {
            placeMark(0, 1);
            drawBoard();
        } else if (move == 3) {
            placeMark(0, 2);
            drawBoard();
        } else if (move == 4) {
            placeMark(1, 0);
            drawBoard();
        } else if (move == 5) {
            placeMark(1, 1);
            drawBoard();
        } else if (move == 6) {
            placeMark(1, 2);
            drawBoard();
        } else if (move == 7) {
            placeMark(2, 0);
            drawBoard();
        } else if (move == 8) {
            placeMark(2, 1);
            drawBoard();
        } else if (move == 9) {
            placeMark(2, 2);
            drawBoard();
        } else {
            System.out.println("Invalid, choose a number between 1-9"); 
            continue; 
        }

    if (checkForWin()) {
        System.out.println("Player " + currentPlayer + " has won!");
        break;
    }

    if (isBoardFull()) {
        System.out.println("It's a tie!");
        break;
    }
    changePlayer();
} while (true);

}

//Empties the board by replacing all X/O with -
public void boardInit() {
    for (int r = 0; r < 3; r++) {
        for (int c = 0; c < 3; c++) {
            board[r][c] = '-';
        }
    }
}

//Draws the board in it's current state
public void drawBoard() {
    System.out.println("+---+---+---+");
    for (int r = 0; r < 3; r++) {
        System.out.print("| ");
        for (int c = 0; c < 3; c++) {
            System.out.print(board[r][c] + " | ");              
        }
        System.out.println();
        System.out.println("+---+---+---+");
    }
    System.out.println("\n-------------------------------------\n");

}

//Place's the current players mark in the indicated position
public void placeMark(int row, int col) {
    if ((row >= 0) && (row < 3)) {
        if ((col >= 0) && (col < 3)) {
            if (board[row][col] == '-') {
                board[row][col] = currentPlayer;    
            } 
        }
    }
}



//switches players
public char changePlayer() {
        if (currentPlayer == 'X') {
            currentPlayer = 'O';
        } else
            currentPlayer = 'X';
    return currentPlayer;
}


//checks whether the board is full or not
public boolean isBoardFull() {
    for (int r = 0; r < 3; r++) {
        for (int c = 0; c < 3; c++) {
            if (board[r][c] == '-') {
            return false;
            }
        }
    }
    return true;
}

//checks whether a win-condition exists or not
public boolean checkForWin() {
    //loops through rows checking if win-condition exists
    for (int r = 0; r < 3; r++) {
        if (board[r][0] == board[r][1] && board[r][1] == board[r][2] && board[r][0] != '-')
            return true;
        }
    //loops through columns checking if win-condition exists
    for (int c = 0; c < 3; c++) {
        if (board[0][c] == board[1][c] && board[1][c] == board[2][c] && board[0][c] != '-' ) 
            return true;
        }
    //checks diagonals for win-condition
    if (board[0][0] == board[1][1] && board[1][1] == board[2][2] && board[0][0] != '-')
        return true;

    if (board[0][2] == board[1][1] && board[1][1] == board[2][0] && board[0][0] != '-')
        return true;

    return false;
}

// prints the instructions at the start of the game
public void welcomeAndInstruct() {
    System.out.println("Welcome to Tic Tac Toe, a 2 player game for console.");
    System.out.println("Two players take turns in marking the squares on a 3 x 3 grid.");
    System.out.println("The player who succeeds in placing three of their marks in a horizontal, vertical or diagonal row wins the game.");
    System.out.println("To select a square on the grid by entering it's corresponding number when prompted, as shown below:");
    System.out.println();

    board[0][0] = '1';
    board[0][1] = '2';
    board[0][2] = '3';
    board[1][0] = '4';
    board[1][1] = '5';
    board[1][2] = '6';
    board[2][0] = '7';
    board[2][1] = '8';
    board[2][2] = '9';

    drawBoard();

    }
}

Debugger should definitely let you see where your logic flaw is. Specifically under your checkForWin() method your last if condition — gtgaxiola

Nahid Nahid · Accepted Answer · 2018-08-06T16:22:03

At :

if (board[0][2] == board[1][1] && board[1][1] == board[2][0] && board[0][0] != '-')

instead of board[0][0] check board[0][2].

Java Tic Tac Toe win-condition

2 Answers