Description : size() function is used to return the size of the queue or the number of elements in the queue.
Example:
std::queue<int> myqueue;
myqueue.push(4);
myqueue.push(5);
myqueue.push(9);
myqueue.push(1);
myqueue.push(3);
// Queue becomes 4, 5, 9, 1, 3
// Print the size of myqueue
std::cout << myqueue.size();