Ulam Spiral

#include <string>
#include <iostream>
#include <cassert>
#include <iomanip>
void print_mat(int** mat, size_t size)
{
    for (size_t i = 0; i < size; i++)
    {
        for (size_t j = 0; j < size; j++)
        {
            std::cout.width(3);
            std::cout << mat[i][j] << ' ';
        }
        std::cout << "\n";
    }
}

void fill_line(int** spiral, size_t posx, size_t posy, int len, bool byX, int& num, bool upright = false)
{
    // limiting bound of array to [0; inf]
    print_mat(spiral, 7);
    std::cout << '\n';
    //assert(!upright || (posx >= len) || !byX);
    //assert(!upright || (posy >= len) || byX);

    if (byX)
    {
        for (int i = 0; i < len; i++)
        {
            int offset = upright ? -i : i;
            spiral[posy][posx + offset] = num;

            num++;
        }

    }
    else
    {

        for (int i = 0; i < len; i++)
        {
            int offset = upright ? -i : i;
            spiral[posy + offset][posx] = num;
            num++;
        }
    }
}
static int num = 2;
void fill_ulam(int** spiral, size_t posx, size_t posy, size_t depth = 1)
{
    // fill up
    fill_line(spiral, posx, posy, depth * 2, false, num, true);
    posy -= depth * 2 - 1;
    posx -= 1;
    // fill left
    fill_line(spiral, posx, posy, depth * 2, true, num, true);
    posx -= depth * 2 - 1;
    posy += 1;
    // fill down
    fill_line(spiral, posx, posy, depth * 2, false, num, false);
    posy += depth * 2 - 1;
    posx += 1;
    // fill right
    fill_line(spiral, posx, posy, depth * 2, true, num, false);
    posx += depth * 2;
    if (depth == 10) return; // recursive end (limit of size of our matrix)
    // recursive continue
    fill_ulam(spiral, posx, posy, depth + 1);

}

int main()
{
    constexpr size_t size = 2*10 + 1;
    int** spiral = new int* [size];
    for (size_t i = 0; i < size; i++) {
        spiral[i] = new int[size] {};

    }
    spiral[size / 2][size / 2] = 1;
    fill_ulam(spiral, size / 2 + 1, size / 2);
    print_mat(spiral, size);

    for (size_t i = 0; i < size; i++) {
        delete[] spiral[i];
    }
    delete[] spiral;

}