C: quicksort fails to sort

[dwrz]

I was trying to understand why my implementation of quicksort was not working, and figured I'd look at this repo for some insights.

The array input that I am testing is:

int nbr[8] = {3, 1, 2, 0, 8, 9, 11, -1};

If I print the elements after sorting, I see:

nbr failed
-1 1 2 0 3 8 9 11 
nbr_small passed
nbr_null passed

0 is at index 4, instead of index 2.

Following is main with my modifications:

int main(void){
  int nbr[8] = {3, 1, 2, 0, 8, 9, 11, -1};
  int nbr_small[2] = {100, 2};
  int *nbr_null = NULL;

  quicksort(nbr, 8);
  quicksort(nbr_small, 2);
  quicksort(nbr_null, 10);

  if(is_sorted(nbr, 8))
    printf("nbr passed\n");
  else
    printf("nbr failed\n");
  for (int i = 0; i < 8; i++) {
	  printf("%d ", nbr[i]);
  }
  printf("\n");

  if(is_sorted(nbr_small, 2))
    printf("nbr_small passed\n");
  else
    printf("nbr_small failed\n");

  if(nbr_null == NULL)
    printf("nbr_null passed\n");
  else
    printf("nbr_null failed\n");

  return EXIT_SUCCESS;
}

Quick diff:

int main(void){						      |	int main(){
  int nbr[8] = {3, 1, 2, 0, 8, 9, 11, -1};		      |	  int i;
							      >	  int nbr[5] = {10, 1, 0, 5, 2};
  quicksort(nbr, 8);					      |	  quicksort(nbr, 5);
  if(is_sorted(nbr, 8))					      |	  if(is_sorted(nbr, 5))
  for (int i = 0; i < 8; i++) {				      <
	  printf("%d ", nbr[i]);			      <
  }							      <
  printf("\n");						      <