queue c 2b 2b

1//Queue is a data structure designed to operate in FIFO(First in First out) context. 
2//In queue elements are inserted from rear end and get removed from front end.
3 The functions supported by queue:
4 ---------------------------------
5 empty()   | Tests whether queue is empty or not.
6 size()    | Returns the total number of elements present in the queue.
7 push()    | Inserts new element at the end of queue.
8 emplace() | Constructs and inserts new element at the end of queue.
9 pop()     | Removes front element of the queue.
10 swap()    | Exchanges the contents of queue with contents of another queue.
11 front()   | Returns a reference to the first element of the queue.
12 back()    | Returns a reference to the last element of queue.