#include <iostream>
#include <queue>

using namespace std;

void test01() {
  queue<int> q;
  q.push(10);
  q.push(20);
  q.push(30);
  q.push(40);

  while (q.empty() == false) {
    cout << " 队头: " << q.front() << endl;
    cout << " 队尾: " << q.back() << endl;
    q.pop();
  }
}

int main() {

  test01();

  return EXIT_SUCCESS;
}