Function main

13. Queue/01_Introduction.cpp:4–32

using namespace std;

int main()
{
	/*
	
	Queue is FIFO (First In First Out) data structure 

		            ------------------------
	dequeue()  <---	10 | 20 | 30 | 40 | 50 | <--- enqueue(x)
		            ------------------------   
                                          
		             ^                   ^
		             |                   |
		             |                   |

		            front               rear

	Operations :

	a.enque(x) : insert
	b.deque() : remove
	c.getfront() : get front element
	d.getrear() : get last element
	e.size() : get current size of queue
	f.isempty() : check if queue empty

	all operations have time comp. O(1)

	*/
}