Question

I’m trying to code a Bingo Board in C++, but I’m doing something very wrong. I’m not sure what, but for whatever reason when I initialize the number of rows and columns, and do a nested for loop on the arrays I created to implement this structure, I get what appears to be more than a hundred rows and 30+ columns, when I should just be getting a five, by five board. I’m also trying to specify a max and min value for my rand function, but it appears that there isn’t a way to do this. Thus, what would be the best approach to accomplish this without giving away the solution? The reason why I mention that last bit is so I can learn how to do this lol.

Here is my code:

#ifndef BOARD_H
#define BOARD_H
#include <cstdlib>
#include <time.h>
#include <stdio.h>

class Board
{
public:
    Board(unsigned int numberOfRows, unsigned int numberOfColumns, unsigned int seed, unsigned int max, unsigned int min);
    void generate();
        void setSeedValue(int seed);

private:
   unsigned int m_rows[];
   unsigned int m_columns[];
   unsigned int m_max, m_min;
};

#endif // BOARD_H

    Board::Board(unsigned int numberOfRows, unsigned int numberOfColumns, unsigned int seed, unsigned int max, unsigned int min)
{
    this->m_rows[numberOfRows];
    this->m_columns[numberOfColumns];
    srand(seed);
    this->m_max = max;
    this->m_min = min;
    printf("%d\n", size_t(m_rows));
    printf("%d\n", size_t(m_columns));
}

void Board::generate()
{
    for (int i = 0; i < size_t(m_rows); i++)
    {
        for(int j = 0; j < size_t(m_columns); j++)
        {
            this->m_columns[j] = (rand() % 10) + j;

            std::cout << this->m_columns[j];
        }
    }
}

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    Board * board = new Board(5, 5, time(NULL), 100, 1);

    board->generate();

    delete board;

    return a.exec();
}

Answer 1

In order to create the 2-dimensional board your wanting, where the size is input at runtime, you’re going to have to actually dynamically allocate a board in memory … you can’t declare your board the way you’ve done in your class as zero-length arrays.

Code like this:

this->m_rows[numberOfRows];

does not initialize your array-size … rather it actually attempts to access memory allocated at that offset from the start of m_rows … that could cause a segmentation fault or some other undefined behavior due to accessing memory beyond the end of the class/structure type.

It would be much better, since you’re using C++, to create your board class using the STL’s std::vector container. Your Board class would then look like the following:

class Board
{
    public:
        Board(unsigned int numberOfRows, unsigned int numberOfColumns, 
              unsigned int seed, unsigned int max, unsigned int min);

        void generate();
        void setSeedValue(int seed);

    private:
       vector<vector<unsigned int> > board; //use the STL vector container
       unsigned int m_max, m_min;
};

Then in your constructor, you would actually allocate the necessary memory (through the STL’s vector container) that your board will take up:

Board::Board(unsigned int numberOfRows, unsigned int numberOfColumns, 
             unsigned int seed, unsigned int max, unsigned int min)
{
    for (int i=0; i < numberOfRows; i++)
    {
        this->board.push_back(vector<unsigned int>(numberOfColumns, 0));
    }

    srand(seed);
    this->m_max = max;
    this->m_min = min;
    printf("%d\n", size_t(m_rows));
    printf("%d\n", size_t(m_columns));
}

Finally, your Board::generate function would now look like the following:

void Board::generate()
{
    for (int i = 0; i < this->board.size(); i++)
    {
        for(int j = 0; j < this->board[i].size(); j++)
        {
            this->board[i][j] = (rand() % 10) + j;

            std::cout << this->board[i][j];
        }
    }
}