heap sort

#include <stdio.h>

void heapify(int* intp, unsigned idx, unsigned nr)
{
    unsigned j = idx;
    while (1) {
        unsigned i = idx * 2 + 1;
        
        if (nr > i && intp[i] > intp[j]) {
            j = i;
        }
        ++i;

        if (nr > i && intp[i] > intp[j]) {
            j = i;
        }

        if (j == idx) {
            break;
        }

        int n = intp[idx];
        intp[idx] = intp[j];
        intp[j] = n;
        idx = j;
    }
}

void make_heap(int* intp, unsigned nr)
{
    unsigned idx = (nr / 2 - 1);
    while (idx != (unsigned) (-1)) {
        heapify(intp, idx, nr);
        idx -= 1;
    }
}

void heap_sort(int* intp, unsigned nr)
{
    do {
        --nr;
        int n = intp[0];
        intp[0] = intp[nr];
        intp[nr] = n;
        heapify(intp, 0, nr);
    } while (nr > 0);
}

int main(void)
{
    int a[] = {6, 9, 2, 4, 0, 3, 8, 1, 5};
    unsigned nr = sizeof(a) / sizeof(a[0]);

    if (nr > 0) {
        make_heap(a, nr);
        heap_sort(a, nr);

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

    return 0;
}