#include <stdio.h>

int sum1D(int n, int arr[]);
void zero(int n, int arr[]);
void zero2D(int n, int m, int arr[][m]);
int *make_array(int n);

int main()
{
  int a[5] = {12, 24, 45, 99, 100};

  int a2d[3][3] = {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}};
  int b2d[3][4];

  zero2D(3, 4, b2d);

  printf("%d\n", sum1D(5, a));
  printf("%d\n", sum1D(3, a2d[1])); // row of 2-D array is a 1-D array
  printf("%d\n", sum1D(4, a2d[1])); // lying about size -- wraps around to next row 
  printf("%d\n", sum1D(3, b2d[0])); // sum is zero, of course, since we zeroed it with zero2D

  int *arr15 = make_array(15);
  printf("%d\n", sum1D(15, arr15));
}

void zero2D(int n, int m, int arr[][m])
{
  for (int r = 0; r < n; r++)
    {
      for (int c = 0; c < m; c++)
	{
	  arr[r][c] = 0;
	}
    }
}

void zero(int n, int *arr) // as a parameter, int arr[] is equiv to int *arr
{
  for (int i = 0; i < n; i++)
    {
      arr[i] = 0;
    }
}

int sum1D(int n, int *arr)
{
  int sum = 0;
  for (int i = 0; i < n; i++)
    {
      sum += arr[i];
    }
  return sum;
}

// The *WRONG* way to write a function that returns an array.
// Note the helpful compiler warning about returning a pointer to
// a local variable -- a variable that is going to get bulldozed at the }
//
//           |7
//        }o===o  someone please draw me a better ASCII-art bulldozer
int *make_array(int n)
{
  int result[n];
  for (int i = 0; i < n; i++)
    {
      result[i] = i;
    }
  return result;
}