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Question

I am getting a "Access violation reading location 0x007CE4F8" (print of the error at the end of the post) right after running and choosing a place to put my marker.

I am a begginer c++ programmer so would love if you could keep the explanation the simplest possible.

main.cpp

    #include <iostream>
    #include "playGame.h"

    using namespace std;

    int main()
    {

        playGame game;
        game.play();

        system("PAUSE");
        return 0;
    }

playGame.cpp

#include "playGame.h"
#include <iostream>

using namespace std;

playGame::playGame()
{
}

bool playGame::play()
{
    char player1 = 'X';
    char player2 = 'O';
    bool gameOver = false;
    int turn = 0;

    char currentPlayer = player1;

    clearBoard();

    while (gameOver == false)
    {
        printBoard();

        x = getX();
        y = getY();

        while (placeMarker(x, y, currentPlayer) == false)
        {
            cout << "***Place already taken!***" << endl;
            x = getX();
            y = getY();
        }
            turn++;

    }
    return gameOver;
}

void playGame::clearBoard()
{
    for (int i = 0; i < 3; i++)
    {
        for (int j = 0; j < 3; j++)
        {
            board[i][j] = ' ';
        }
    }
}

void playGame::printBoard()
{
    cout << endl;
    cout << " |1 2 3|\n";
    for (int i = 0; i < 3; i++) {
        cout << " -------\n";
        cout << i + 1 << "|" << board[i][0] << "|" << board[i][1] << "|" << board[i][2] << "|\n";
    }
    cout << " -------\n";
}

int playGame::getX()
{
    while ((x < 1) || (x > 3)) {
        cout << "Choose X coordinate (1 - 3): ";
        cin >> x;
        if ((x < 1) || (x > 3))
        {
            cout << "Bad input" << endl;
        }
        else
        {
            x--;
            return x;
        }
    }

}

int playGame::getY()
{
    while ((y < 1) || (y > 3)) {
        cout << "Choose Y coordinate (1 - 3): ";
        cin >> y;
        if ((y < 1) || (y > 3))
        {
            cout << "Bad input" << endl;
        }
        else
        {
            y--;
            return y;
        }
    }
}

bool playGame::placeMarker(int x, int y, char currentPlayer)
{
    if (board[y][x] != ' ')
    {
        return false;
    }
        board[y][x] = currentPlayer;
        return true;
}

playGame.h

#pragma once
#include <iostream>

using namespace std;

class playGame
{
public:
    playGame();
    bool play();

private:
    void clearBoard();
    void printBoard();
    int getX();
    int getY();
    bool placeMarker(int x, int y, char currentPlayer);

    char board[3][3];
    int x, y;

};

Posting a print if makes your lives better: Image of the error

Answer 1

I see couple of problems:

1. You haven't initialized the member variables of playGame in the constructor. Using values of uninitialized member variables is cause for undefined behavior.

2. You don't have a return statement in all branches of getX() and getY() . That is cause for undefined behavior.

Update the constructor to have sensible initial values.

playGame::playGame() : x(0), y(0)
{
   for ( int i = 0; i < 3; ++i )
   {
      for ( int j = 0; j < 3; ++j )
      {
         board[i][j] = ' ';
      }
   }
}

Update getX() to:

int playGame::getX()
{
   // Make x invalid before starting the while loop.
   // Otherwise, the last valid value will be returned.
   x = 0;
   while ((x < 1) || (x > 3))
   {
      cout << "Choose X coordinate (1 - 3): ";
      cin >> x;
      if ((x < 1) || (x > 3))
      {
         cout << "Bad input" << endl;
      }
   }

   x--;
   return x;
}

Update getY() similarly.

Answer 2

在构造函数中将x和y初始化为例如0（超出1-3的范围），并在放置标记后将它们重置为0。

Answer 3

I don't know if this can explain your problem but in your code I see a thing that I found a little weird.

You define x and y as members of the playGame class.

So, when in play() you write

    x = getX();
    y = getY();

and in getX() and getY() you write

    return x;

and

    return y;

you're copying member x in member x through getX() and member y in member y through getY() .

Suggestion: delete x and y members from playGame class and define x and y as local variables in methods.

Answer 4

Protect your function placeMarker to be sure that your are not out of bounds when you access to your array, ie:

if(x > MAX_X || x< MIN_X) return false;
if(y > MAX_Y || y< MIN_Y) return false;