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Queue In C++

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.

Fig:Queue In C++

 

The functions supported by queue are :

 

1.   empty() – Returns whether the queue is empty.

 

       2.   size() – Returns the size of the queue.

 

3.   queue ::swap()-Exchange the contents of two queues but the queues must be of same type, although sizes may differ.

 
4.   queue::emplace()-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()– 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(q) and pop() – push() function adds the element ‘g’ at the end of the queue. pop() function deletes the first element of the queue.

 

Program:

#include <iostream>

#include <queue>

void showq(queue <int> gq)

{

          queue <int> g = gq;

          while (!g.empty())

          {

                   cout << '\t' << g.front();

                   g.pop();

          }

          cout << '\n';

}

int main()

{

          queue <int> gquiz;

          gquiz.push(10);

          gquiz.push(20);

          gquiz.push(30);

          cout << "The queue gquiz is : ";

          showq(gquiz);

          cout << "\ngquiz.size() : " << gquiz.size();

          cout << "\ngquiz.front() : " << gquiz.front();

          cout << "\ngquiz.back() : " << gquiz.back();

          cout << "\ngquiz.pop() : ";

          gquiz.pop();

          showq(gquiz);

          return 0;

}

Output:

The queue gquiz is: 10     20     30

gquiz.size():3

gquiz.front():10

gquiz.back(): 30

gquiz.pop(): 20  30