Question

My question is why did they use (int**) in the declaration of the matrix pointer as a pointer to an array. Is it necessary? What difference does it make?

#include <iostream>
using namespace std;
int main()
{
    int **matrix;       // Pointer to matrix
    matrix = (int **) new int *[2]; // Why use (int**) is it necessary?
    for (i = 0; i < 2; i++)
        matrix[i] = new int[2];
    for (i = 0; i < 2; i++)
        for (int j = 0; j < 2; j++) {
            matrix[i][j] = j + i;
        }
}

Answer 1

It’s unnecessary and potentially dangerous.

The type of the new-expression is already int**, suitable for assigning to matrix. There is no need to convert it to its own type.

One should not use C-style casts even when a conversion is necessary. Doing so will force a conversion even if it makes no sense, which is a very good way to hide errors; for example, if you accidentally new the wrong type:

matrix = new int[2];           // Friendly compiler error
matrix = (int**) new int[2];   // No diagnostic, likely to cause weird
                               // run-time errors.