#include <stdlib.h>
#include <stdio.h>

// max total size of statically allocated arrays is platform-dependent
// (platform = OS + hardware, so Linux+Intel or macOs+Mac or Android+ARM)
#define MAX_STATIC 1000000

int sum2D(int w, int h, int arr[][w]);

// a function that takes an int and returns a pointer to an x-by-4 array
// that 4 must be a constant expression, though
int (*make2D(int n))[4];

/**
 * An example of dynamically allocated rectangular 2-D arrays.
 */

int main(int argc, char *argv[])
{
  // [Bill & Ted voice] WHOA!
  int h = 3;
  int w = 4;
  int (*arr)[w]; // a pointer to an x-by-w array (x can be anything)

  arr = malloc(sizeof(int) * w * h);
  for (int i = 0; i < h; i++)
    {
      for (int j = 0; j < w; j++)
	{
	  arr[i][j] = i + j;
	}
    }
  printf("arr = %p\n", arr);
  printf("&arr = %p\n", (void *)&arr);
  printf("arr[0] = %p\n", arr[0]);
  printf("arr[1] = %p\n", arr[1]);
  printf("arr[2] = %p\n", arr[2]);
  printf("sum2D(arr) = %d\n", sum2D(w, h, arr));

  free(arr);

  int (*a2)[4] = make2D(6);
  printf("sum2D(a2) = %d\n", sum2D(4, 6, a2));
  free(a2);
}

int sum2D(int w, int h, int arr[][w])
{
  int sum = 0;
  for (int r = 0; r < h; r++)
    {
      for (int c = 0; c < w; c++)
	{
	  sum += arr[r][c];
	}
    }
  return sum;
}

int (*make2D(int n))[4]
{
  int (*arr)[4] = malloc(sizeof(int) * n * 4);
  for (int r = 0; r < n; r++)
    {
      for (int c = 0; c < 4; c++)
	{
	  arr[r][c] = r + c;
	}
    }
  return arr;
}