max heap c++ stl;

priority_queue <int> maxHeap; 

// C++ program to show that priority_queue is by 
// default a Max Heap 
#include <bits/stdc++.h> 
using namespace std; 

// Driver code 
int main () 
{ 
	// Creates a max heap 
	priority_queue <int> pq; 
	pq.push(5); 
	pq.push(1); 
	pq.push(10); 
	pq.push(30); 
	pq.push(20); 

	// One by one extract items from max heap 
	while (pq.empty() == false) 
	{ 
		cout << pq.top() << " "; 
		pq.pop(); 
	} 

	return 0; 
} 

// C++ code to demonstrate the working of  
// push_heap() and pop_heap() 
#include<bits/stdc++.h>  
using namespace std; 
int main() 
{ 
      
    // Initializing a vector 
    vector<int> v1 = {20, 30, 40, 25, 15}; 
      
    // Converting vector into a heap 
    // using make_heap() 
    make_heap(v1.begin(), v1.end()); 
      
    // Displaying the maximum element of heap 
    // using front() 
    cout << "The maximum element of heap is : "; 
    cout << v1.front() << endl; 
      
    // using push_back() to enter element 
    // in vector 
    v1.push_back(50); 
      
    // using push_heap() to reorder elements 
    push_heap(v1.begin(), v1.end()); 
      
    // Displaying the maximum element of heap 
    // using front() 
    cout << "The maximum element of heap after push is : "; 
    cout << v1.front() << endl; 
      
     // using pop_heap() to delete maximum element 
    pop_heap(v1.begin(), v1.end()); 
    v1.pop_back(); 
      
    // Displaying the maximum element of heap 
    // using front() 
    cout << "The maximum element of heap after pop is : "; 
    cout << v1.front() << endl; 
      
    return 0; 
} 

#include <iostream>
using namespace std;
void max_heap(int *a, int m, int n) {
   int j, t;
   t = a[m];
   j = 2 * m;
   while (j <= n) {
      if (j < n && a[j+1] > a[j])
         j = j + 1;
      if (t > a[j])
         break;
      else if (t <= a[j]) {
         a[j / 2] = a[j];
         j = 2 * j;
      }
   }
   a[j/2] = t;
   return;
}
void build_maxheap(int *a,int n) {
   int k;
   for(k = n/2; k >= 1; k--) {
      max_heap(a,k,n);
   }
}
int main() {
   int n, i;
   cout<<"enter no of elements of array\n";
   cin>>n;
   int a[30];
   for (i = 1; i <= n; i++) {
      cout<<"enter elements"<<" "<<(i)<<endl;
      cin>>a[i];
   }
   build_maxheap(a,n);
   cout<<"Max Heap\n";
   for (i = 1; i <= n; i++) {
      cout<<a[i]<<endl;
   }
}