Heap Sort

#include <stdio.h>
#include <stdlib.h>
int heapsize;
void swap(int *a ,int *b){
    int temp = *a;
    *a = *b;
    *b = temp;
}
void max_heapify(int *a, int i){
    int l = 2*i, r = l+1, largest;
    if(l < heapsize && a[l] > a[i]) largest = l;
    else largest = i;
    if(r < heapsize && a[r] > a[largest]) largest = r;
    if(largest != i){
        swap(&a[i], &a[largest]);
        max_heapify(a, largest);
    }
}
void build_max_heap(int *a){
    for(int i = heapsize/2; i >= 0; i--) max_heapify(a, i);
}
void heapsort(int *a){
    build_max_heap(a);
    for(int i = heapsize-1; i >= 1; i--){
        swap(&a[0], &a[i]);
        heapsize--;
        max_heapify(a, 0);
    }
}
int main(){
    int i, n;
    printf("Number of elements:  ");
    scanf("%d", &n);
    heapsize = n;
    int *a = (int*)malloc(sizeof(int) * n);
    for(i = 0; i < n; i++)  scanf("%d", &a[i]);
    heapsort(a);
    for(i = 0; i < n; i++) printf("\t%d\t", a[i]);
    return 0;
}