How to fill a matrix (two-dimensional array)?

Question

C++ / C#

Task: fill the matrix (two-dimensional array) with the values ​​of the vector b1, b2,...,b81 from the center in a spiral (left-down-right-up).

Note: the figure shows the index values!
I wrote a code that just fills the matrix in the normal way:

#include <iostream>
using namespace std;

int main()
{
  const int rows = 9;
  const int cols = 9;
  int ARR[rows][cols];

  for (int i = 0; i < rows; i++)
  {
    for (int j = 0; j < cols; j++)
    {
      ARR[i][j] = rand() % 10;
    }
  }

  for (int i = 0; i < rows; i++)
  {
    for (int j = 0; j < cols; j++)
    {
      cout << ARR[i][j] << "  ";
    }
    cout << endl;
  }
}

How can I make the indexes of the elements increase from the center in a spiral (as shown in the figure)?

Answer 1

Find the index - the center of the matrix. Shift the index to the left by one. Then down one. Then right one. Then up two. Then left two. Etc.