Priority Queue Using Heap

#include <stdio.h>
#include <stdlib.h>
struct entity{ //An entity consists has its data and its priority
    int data;
    int priority;
};
int heapsize;
void swap(int *a ,int *b){
    int temp = *a; *a = *b; *b = temp;
}
void min_heapify(struct entity a[], int p){
    int r = (p+1)*2, l=r-1, smallest = p; //p is parent, r is right child and l is left child
    if(l < heapsize && a[l].priority < a[p].priority) smallest = l;
    if(r < heapsize && a[r].priority < a[smallest].priority) smallest = r;
    if(smallest != p){
        swap(&a[p].data, &a[smallest].data); //swap child and parent if parent isn't the smallest
        swap(&a[p].priority, &a[smallest].priority);
        min_heapify(a, smallest); //Keep on calling same method until parent is the smallest
    }
}
void build_min_heap(struct entity a[]){
    for(int p = heapsize/2; p >= 0; p--) min_heapify(a, p);//heapsize/2+1 onwards are leaves
}
void heapsort(struct entity a[]){
    build_min_heap(a);//smallest priority will be at root
    for(int i = heapsize-1; i >= 1; i--){
        swap(&a[0].priority, &a[i].priority); //swap root and a[i]
        swap(&a[0].data, &a[i].data); //root may violate heap property, but children are minheaps
        heapsize--;//delete the element from the heap by decrementing the heap size
        min_heapify(a, 0);//Run minheapify as the heap might violate the heap property.
    }
}
int main(){
    int i, n;
    printf("Enter the size of the Queue: ");
    scanf("%d", &n);
    heapsize = n;
    struct entity *a = (struct entity*)malloc(sizeof(struct entity) * n);
    for(i = 0; i < n; i++){
        printf("\nEnter the number and its priority:-\n");
        scanf("%d%d", &a[i].data, &a[i].priority);
    }
    heapsort(a);
    for(int i = 0; i < n; i++)
        printf("\n%d\t(priority: %d)\n", a[i].data, a[i].priority);
}