K-pairs with smallest sum in 2 arrays in C.

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

struct Pair
{
  int x;
  int y;
  int sum;
};

void swap (struct Pair *a, struct Pair *b)
{
  struct Pair t = *a;
  *a = *b;
  *b = t;
}

void minHeapify (struct Pair arr[], int n, int i)
{
  int smallest = i;
  int l = 2 * i + 1;
  int r = 2 * i + 2;

  if (l < n && arr[l].sum < arr[smallest].sum)
    {
      smallest = l;
    }

  if (r < n && arr[r].sum < arr[smallest].sum)
    {
      smallest = r;
    }
  if (smallest != i)
    {
      swap (&arr[i], &arr[smallest]);
      minHeapify (arr, n, smallest);
    }
}

void buildMinHeap (struct Pair arr[], int n)
{
  for (int i = n / 2 - 1; i >= 0; i--)
    {
      minHeapify (arr, n, i);
    }
}

struct Pair minHeapExtractMin (struct Pair arr[], int *n)
{
  struct Pair min = arr[0];
  arr[0] = arr[*n - 1];
  (*n)--;
  minHeapify (arr, *n, 0);
  return min;
}

void minHeapInsert (struct Pair arr[], int *n, struct Pair key)
{
  (*n)++;
  int i = *n - 1;
  arr[i] = key;

  while (i != 0 && arr[(i - 1) / 2].sum > arr[i].sum)
    {
      swap (&arr[i], &arr[(i - 1) / 2]);
      i = (i - 1) / 2;
    }
}

void kSmallestPairs (int arr1[], int m, int arr2[], int n, int k)
{
  if (m <= 0 || n <= 0 || k <= 0)
    {
      return;
    }
  if (k > m * n)
    {
      k = m * n;
    }

  struct Pair heap[m];
  int heapSize = 0;

  for (int j = 0; j < n; j++)
    {
      struct Pair p = { arr1[0], arr2[j], arr1[0] + arr2[j] };
      minHeapInsert (heap, &heapSize, p);
    }

  for (int i = 0; i < k; i++)
    {
      struct Pair p = minHeapExtractMin (heap, &heapSize);
      printf ("(%d, %d) ", p.x, p.y);

      if (p.x < m - 1)
	{
	  struct Pair next = { arr1[p.x + 1], p.y, arr1[p.x + 1] + p.y };
	  minHeapInsert (heap, &heapSize, next);
	}
    }
}

int main ()
{
  int arr1[] = { 1, 7, 11 };
  int m = sizeof (arr1) / sizeof (arr1[0]);

  int arr2[] = { 2, 4, 6 };
  int n = sizeof (arr2) / sizeof (arr2[0]);

  int k = 3;

  kSmallestPairs (arr1, m, arr2, n, k);

  return 0;
}