Quicksort algorithm implemented in C

quicksort.c

#include <stdio.h>

#define swap(a, b) {int aux = a; a = b; b = aux;}

void quicksort(int*, int, int);
int partition(int*, int, int);

int main() {
	int a[] = {10,9,8,7,6,5,4,3,2,1};

	quicksort(a, 0, 9);

	for (int i = 0; i < 10; i++) {
		printf("%d ", a[i]);
	}

	return 0;
}

void quicksort(int *array, int p, int r) {
	if (p < r) {
		int q = partition(array, p, r);
		quicksort(array, p, q-1);
		quicksort(array, q+1, r);
	}
}

int partition(int *array, int p, int r) {
	int x = array[r];
	int i = p-1;
	for (int j = p; j < r; j++) {
		if (array[j] <= x) {
			i++;
			swap(array[i], array[j]);
		}
	}
	swap(array[i+1], array[r]);

	return i+1;
}