How to build a dynamic 2d array inside a constructor? - c++

Question

Building a Memory game. Users can input the number of cards they would like to deal on their 'board'. I am taking that input number(int size) and building a 2d array of objects as the game board, which is stored in a constructor. My next step after getting this to work will be to replace the array elements with 'dealt' card objects to display. **Receiving initialization for the arrays and am curious why. Do you have any suggestions as to why or better ways to write this? **
.cpp file relvant code
#include <iostream>
#include "GameBoard.h"
#include <math.h>
using namespace std;
GameBoard::GameBoard(int size)
{
if (size % 2 != 0)
{
size++;
}
int row;
int col;
row = 4;
col = ceil(size/4);
Card gameBoard = new Card*[row];
int i;
for(i=0; i<row; i++){
Card gameBoard[i] = new Card[col];
}
.h file
#ifndef GameBoard_h
#define GameBoard_h
#include "Deck.h"
#include <iostream>
using namespace std;
class GameBoard{
private:
Card **gameBoard;
Deck deck;
Card card;
int CardsToDeal;
public:
GameBoard(int size);
GameBoard();
void initializeBoard();
};
#endif

Answer 1

If you know the size at compile-time, use std::array. When you don't use std::vector. These can of course be nested, like:
std::array<std::vector<Card>, 4> gameBoard;
If the number or "rows" are small you can initialize directly in the constructor initializer list:
GameBoard::GameBoard(int size)
: gameBoard {
std::vector<Card>(std::ceil(size / 4.0)),
std::vector<Card>(std::ceil(size / 4.0)),
std::vector<Card>(std::ceil(size / 4.0)),
std::vector<Card>(std::ceil(size / 4.0))
}
{
// Rest of constructor...
}
Otherwise let the array default-construct and set up the vectors inside the constructor body in a loop:
GameBoard::GameBoard(int size)
{
int columns = std::ceil(size / 4.0);
for (auto& card_vector : gameBoard)
{
card_vector.resize(columns);
}
// Rest of constructor...
}