Sort Heap

#include <fstream>
using namespace std;
ifstream f("heap_sort.in");
ofstream g("heap_sort.out");
int n, a[1000001];

void heapU(int a[],int n,int i)
{
    int larg=i;
    int st=2*i+1,dr=2*i+2;
    if(st<n&&a[st]>a[larg])
        larg=st;
    if(dr<n&&a[dr]>a[larg])
        larg=dr;
    if(larg!=i)
        swap(a[i], a[larg]),heapU(a,n,larg);
}

void heapSort(int a[],int n)
{
    for(int i=n/2-1;i>=0;--i)
        heapU(a,n,i);
    for(int i=n-1;i>=0;--i)
        swap(a[0], a[i]),heapU(a,i,0);
}

int main()
{
    f>>n;
    for(int i=0;i<n;++i)
        f>>a[i];
    heapSort(a,n);
    for(int i=0;i<n;++i)
        g<<a[i]<<' ';
    return 0;
}