Question

So I was working on a Tic-Tac-Toe game and for my input function I was getting the move the player made to store as an integer in a 2d array, the input is gotten using a reference to a 1D array of pointers to positions in the 2D array.

However my problem is, when I seem to set the value of the multi-dimensional array’s square to something by using a pointer, nothing happens.

Here is the input function:

void Game::input(Board b){
int *spots[9]; // Possible spots for the input
bool validInput = false;
spots[0] = &b.board[2][0];
spots[1] = &b.board[2][1];
spots[2] = &b.board[2][2];
spots[3] = &b.board[1][0];
spots[4] = &b.board[1][1];
spots[5] = &b.board[1][2];
spots[6] = &b.board[0][0];
spots[7] = &b.board[0][1];
spots[8] = &b.board[0][2];
redo:
    cout << ">> " << endl;
    int input; // Input
    cin >> input; // Get the input
    validInput = cin;
    if(!validInput){
        cout << "Numbers only please!" << endl;
        cin.clear();
        while(cin.get() != '\n');
        goto redo;
    }
    if(input > 9 || input <= 0){
        cout << "Invalid move!" << endl;
        goto redo;
    }
    input--; // Subtract 1 for array location
    if(*spots[input] != 0){
        cout << "Square is already being used!" << endl;
        goto redo;
    }
    *spots[input] = 1;
}

Now, say I input the number 7. It should set b.board[0][0] to 1. However this doesn’t seem to happen. When I run a unit case afterwards, the board[0][0] doesn’t seem to be set to 1, and it doesn’t reflect in my array. Am I messing something up about pointers here?

Answer 1

The argument to your function is passed by value and therefore any changes you make to it are not recognized since pass by value creates a copy of the argument. Consider passing by pointer or reference instead.