Learning about function pointers in C by implementing bubble sort with a comparator

bubble-fptr.c

#include <stdio.h>

int sort_by_asc(int a, int b)
{
	if(a < b) return 0;
	return 1;
}

int sort_by_dsc(int a, int b)
{
	if(a > b) return 0;
	return 1;
}

typedef int (*comparator)(int,int);

void bubble_sort(int* arr, int length, comparator cmp)
{
	int i, j;
	for(i = 0; i < length - 1; ++i)
	{
		int flag = 1;
		for(j = 0; j < length - i - 1; ++j)
		{
			if(cmp(arr[j], arr[j+1])) // if(arr[j] > arr[j+1])
			{
				int tmp = arr[j];
				arr[j] = arr[j+1];
				arr[j+1] = tmp;
				flag = 0;
			}
		}

		printf("iteration!\n");
		if(flag) break;
	}
}

int main(int argc, char const *argv[])
{
	int arr[] = { 3, 5, -2, 4, 4, 1 };

	bubble_sort(arr, 5, sort_by_asc);

	for(int i = 0; i < 5; ++i) printf("%d ", arr[i]);
	printf("\n");

	return 0;
}