c++ - Invalid use of void expression with a Queue and .pop()

Question

I am trying to make it so that I can pop elements from one queue into a new queue and keep getting that error for this first line of code "temp.push(Q.pop());".

It is something fundamental I am missing so can it be pointed out?

#include <iostream>
#include <queue>
#include <stack>
using namespace std;

void Halves(queue<int>& Q)
{
    stack<int> reverse;
    queue<int> temp;
    for (int i=0; i < Q.size()/2 ; i++)
    {
        temp.push(Q.pop());
    }
    for (int i=0; i < Q.size(); i++)
    {
        reverse.push(Q.pop());
    }
    for (int i=0; i < reverse.size(); i++)
    {
        Q.push(reverse.pop());
    }
    for (int i=0; i < temp.size(); i++)
    {
        Q.push(temp.pop());
    }
    copy(Q);
}

Answer 1

The return type of std::queue::pop() is void. Hence, you may not use:

reverse.push(Q.pop());

You can use:

reverse.push(Q.front());
Q.pop();