Queue in C++ STL

Queues are a type of container adaptors which operate in a first in first out (FIFO) type of arrangement. Elements are inserted at the back (end) and are deleted from the front.

Syntax:
queue< object_type >  queue_name;

Queue functions are:

1. empty() – Returns whether the queue is empty.
2. size() – Returns the size of the queue.
3. queue::swap() in C++ STL – Exchange the contents of two queues but the queues must be of same type, although sizes may differ.
4. queue::emplace() in C++ STL – Insert a new element into the queue container, the new element is added to the end of the queue.
5. queue::front() and queue::back() in C++ STL – front() function returns a reference to the first element of the queue. back() function returns a reference to the last element of the queue.
6. push(g) and pop() – push() function adds the element ‘g’ at the end of the queue. pop() function deletes the first element of the queue.

// Queue in Standard Template Library (STL)
#include <iostream>
#include <queue>

using namespace std;

void showQueue(queue<int> tcp_queue)
{
	queue<int> tsp = tcp_queue;
	while (!tsp.empty()) {
		cout << '\t' << tsp.front();
		tsp.pop();
	}
	cout << '\n';
}
int main()
{
	queue<int> tsp_queue;
	tsp_queue.push(10);
	tsp_queue.push(20);
	tsp_queue.push(30);

	cout << "The queue tsp_queue is : ";
	showQueue(tsp_queue);

	cout << "\ntsp_queue.size() : " << tsp_queue.size();
	cout << "\ntsp_queue.front() : " << tsp_queue.front();
	cout << "\ntsp_queue.back() : " << tsp_queue.back();

	cout << "\ntsp_queue.pop() : ";
	tsp_queue.pop();
	showq(tsp_queue);

	return 0;
}

/*
Output : 
The queue gquiz is :     10    20    30

gquiz.size() : 3
gquiz.front() : 10
gquiz.back() : 30
gquiz.pop() :     20    30
*/