Queue
The std::queue follows the FIFO principle (First In First Out). The queue que, which needs the header <queue>, has four special methods.
With que.push(e) you can insert an element e at the end of the queue and remove the first element from the queue with que.pop(). que.back() enables you to refer to the last element in the que, que.front() to the first element in the que. std::queue has similar characteristics as std::stack. So you can compare std::queue instances and get their sizes. The operations of the queue have constant complexity.
std::queue// queue.cpp
...
#include <queue>...
std::queue<int> myQueue;
std::cout << myQueue.empty() << std::endl; // true
std::cout << myQueue.size() << std::endl; // 0
myQueue.push(1);
myQueue.push(2);
myQueue.push(3);
std::cout << myQueue.back() << std::endl; // 3
std::cout << myQueue.front() << std::endl; // 1
while (!myQueue.empty()){
...