Using methods on pointers to objects in C

Question

I am trying to make a console version of Minesweeper, but I'm having a bit of difficulity with editing the particular cells on the board. As you can see, I have a Board which has a private [6][6] array of Cell objects.

At the moment, I'm trying to call the Cell methods with something like Board gameBoard; gameBoard.accessCell(row,col).flag(); but this seems to not be actually editing the state of the accessed Cell because the object is being copied over rather than a pointer. How can I fix Board::accessCell(int row, int col) to return a pointer to the object so that I can call a function and actually edit its state?

#include <iostream>
#include <ctime>
#include <cstdlib>
#include <iomanip>
#include <string>
using namespace std;

#define debugging true //set this to true to activiate debugging

const int ROWS(6), COLS(6), MINE(-1);
const char FLAG('F'), REVEALED('R'), HIDDEN('*');

class Cell
{
    friend class Board;
    private:
        char displaySetting;
        int minesTouching;
    public:
        Cell();
        int getMinesTouching() const;
        void increaseMinesTouching();
        char getDisplaySetting() const;
        bool isMine() const;
        void flag();
        void reveal();
        void setMine();
};
int Cell::getMinesTouching() const { return this->minesTouching; }
void Cell::increaseMinesTouching() { this->minesTouching++; }
char Cell::getDisplaySetting() const { return this->displaySetting; }
bool Cell::isMine() const { return this->minesTouching == MINE; }
void Cell::flag() { this->displaySetting = FLAG; }
void Cell::reveal() { this->displaySetting = REVEALED; }
void Cell::setMine() { this->minesTouching = MINE; }
Cell::Cell():
    displaySetting(HIDDEN),
    minesTouching(0)
{}

class Board
{
    private:
        Cell boardCells[ROWS][COLS];
    public:
        Board();
        bool isInBounds(int row, int col) const;
        void reveal(int row, int col);
        void displayBoard() const;
        Cell accessCell(int row, int col) const;
};
Board::Board()
{
    //place mines randomly
    srand(time(0));
    for(int i=0; i<6;)
    {
        int row = rand()%6, col = rand()%6;
        if(!this->boardCells[row][col].isMine())
        {
            this->boardCells[row][col].setMine();
            i++;
        }
    }

    //determine number of mines touching each space and store them
    for(int i=0; i<ROWS; i++)
    {
        for(int j=0; j<COLS; j++)
        {
            if(!boardCells[i][j].isMine())
            {
                if(boardCells[i+1][j+1].isMine())   boardCells[i][j].increaseMinesTouching(); //bottom right
                if(boardCells[i-1][j-1].isMine())   boardCells[i][j].increaseMinesTouching(); //top left
                if(boardCells[i+1][j+0].isMine())   boardCells[i][j].increaseMinesTouching(); //down
                if(boardCells[i+0][j+1].isMine())   boardCells[i][j].increaseMinesTouching(); //right
                if(boardCells[i-1][j-0].isMine())   boardCells[i][j].increaseMinesTouching(); //up
                if(boardCells[i-0][j-1].isMine())   boardCells[i][j].increaseMinesTouching(); //left
                if(boardCells[i+1][j-1].isMine())   boardCells[i][j].increaseMinesTouching(); //bottom left
                if(boardCells[i-1][j+1].isMine())   boardCells[i][j].increaseMinesTouching(); //top right
            }
        }
    }
}
bool Board::isInBounds(int row, int col) const
{
    if(row < 0) return false;
    if(row >= ROWS) return false;
    if(col >= COLS) return false;
    if(col < 0) return false;
    return true;
}
void Board::reveal(int row, int col)
{
    if(!this->boardCells[row][col].getMinesTouching())
    {
        this->boardCells[row][col].reveal();
            if(isInBounds(row+1, col+1))    this->reveal(row+1, col+1); //bottom right
        if(isInBounds(row-1, col-1))    this->reveal(row-1, col-1); //top left
        if(isInBounds(row+1, col+0))    this->reveal(row+1, col+0); //down
        if(isInBounds(row+0, col+1))    this->reveal(row+0, col+1); //right
        if(isInBounds(row-1, col-0))    this->reveal(row-1, col-0); //up
        if(isInBounds(row-0, col-1))    this->reveal(row-0, col-1); //left
        if(isInBounds(row+1, col-1))    this->reveal(row+1, col-1); //bottom left
        if(isInBounds(row-1, col+1))    this->reveal(row-1, col+1); //top right
    }
}
void Board::displayBoard() const
{
    system("clear");
    if(debugging) //display system board if debugging is enabled
    {
        for(int i=0; i<ROWS; i++)
        {
            for(int j=0; j<COLS; j++)
                cout << "[ " << setw(3) << this->boardCells[i][j].getMinesTouching() << setw(3) << " ]";
            cout << "\n";
        }
        cout << "\n\n\n";
    }

    //
    for(int i=0; i<ROWS; i++)
    {
        for(int j=0; j<COLS; j++)
        {
            if(this->boardCells[i][j].getDisplaySetting() == HIDDEN)
                cout << "[ " << setw(3) << this->boardCells[i][j].getDisplaySetting() << setw(3) << " ]";
            else if(this->boardCells[i][j].getDisplaySetting() == REVEALED)
                cout << "[ " << setw(3) << this->boardCells[i][j].getMinesTouching() << setw(3) << " ]";
            else
                cout <<"[ " << setw(3) << FLAG << setw(3) << " ]";
        }
        cout << "\n";
    }
    cout << "\n";
}
Cell Board::accessCell(int row, int col) const { return this->boardCells[row][col]; }

//function prototypes
void provideMenu();
string playTurn(Board gameBoard, int& guesses);
void playGame();

int main()
{
    Board gameBoard;
    provideMenu();
    return 0;
}

void provideMenu()
{
    int choice(0);
    while(choice < 1 || choice > 3)
    {
        cout << "1:\t Play a game of Minesweeper" << endl;
        cout << "2:\t Help" << endl;
        cout << "3:\t Exit" << endl;
        cin>>choice;
    }
    switch(choice)
    {
        case 1:
            playGame();
            break;
        case 2:
            cout << "The objective of Minesweeper is to clear all the tiles on the board without mines without uncovering any hidden mines" << endl;
            cout << "*\t Hidden tile, has yet to be revealed" << endl;
            cout << "F\t Flagged tile, marked by user as possible mine" << endl;
            cout << "#\t Any number represents the number of mines touching the tile" << endl;
            break;
    }
}

void playGame()
{
    Board gameBoard;
    int guesses(0);
    string gameState = "onGoing";
    while(gameState == "onGoing")
    {
        gameState = playTurn(gameBoard, guesses);
        if(gameState == "userWon")
            cout << "Congratulations, you've one!" << endl;
        if(gameState == "userLost")
        {
            cout << "Game over! Try again!" << endl;
            gameBoard.displayBoard();
        }
    }
}

string playTurn(Board gameBoard, int& guesses)
{
    gameBoard.displayBoard();

    int row;
    do
    {
        cout << "Row:";
        cin>>row;
    } while(row <0 || row >= ROWS);

    int col;
    do
    {
        cout << "Column:";
        cin>>col;
    } while(col < 0 || col>= COLS);

    if(gameBoard.accessCell(row, col).isMine())
        return "userLost";
    if(++guesses == ROWS*COLS-6)
        return "userWon";
    gameBoard.reveal(row,col);
    return "onGoing";
}

This is far too much code for a Stack Overflow question. Please create a much smaller test-case that is representative of your problem. — Oliver Charlesworth
– Oliver Charlesworth, Commented Jul 17, 2012 at 0:13
Your constructor calls isMine on objects that don't exist because they're outside the range of the array. — David Schwartz
– David Schwartz, Commented Jul 17, 2012 at 0:18

jxh · Accepted Answer · 2012-07-17 00:22:41Z

4

You have defined your access method to return a copy:

    Cell accessCell(int row, int col) const ;

Since you want to be able to modify the Cell that is returned, you should return a reference instead, and the method should not be const.

    Cell & accessCell(int row, int col);

The corresponding changes need to be done to your implementation of the method also.

Cell & Board::accessCell(int row, int col) { return this->boardCells[row][col]; }

answered Jul 17, 2012 at 0:22

jxh

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Comments

Chad · Accepted Answer · 2012-07-17 00:22:51Z

0

Return a reference to the Cell object instead of a copy:

const Cell& Board::accessCell(int row, int col) const
{
    return this->boardCells[row][col];
}

If you need a mutable version (non-const), then I will hint to you that you need to overload this function.

answered Jul 17, 2012 at 0:22

Chad

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