C++ Queue STL

The C++ Queue is a container adapter that gives the programmer a FIFO (first-in, first- out) data structure.

As you see in the above animation the box which goes in first is getting processed first (ie. first-in, first-out) than others and so own.

Queue Constructor

• back - return a reference iterator to the last element of a queue

• empty - returns true(1) if the queue has no element else return false (0)

• front - returns a reference iterator to the first element of a queue

• pop - removes the first element from a queue

• push - adds an element to the end of the queue

• size - returns the number of the elements in the queue

Below is the implementation of the Queue Constructor.

#include<iostream>

#include<queue>

using namespace std;

int main(){

queue<int> q; // Creating a queue "q" of type integer.

// to insert data into the queue use push()

cout<<"Inserting 1,2,3,4,5 in queue\n";

q.push(1);

q.push(2);

q.push(3);

q.push(4);

q.push(5);

// Now we will check whether the queue is empty or not. 

        // (0-false/1-true)

cout<<"Is queue empty: "<<q.empty()<<"\n";

// Checking number of items in queue

cout<<"Number of items present in Queue: "<<q.size()<<"\n";

// Queue cannot be iterated like array or vectors.

int front_data = q.front();

cout<<"Data at front: "<<front_data<<"\n";

// to remove data from front positon we use pop()

q.pop();

// now front_data

front_data = q.front();

cout<<"Data at front_data: "<<front_data<<"\n";

// Printing all the remaining data in queue till queue get empty.

cout<<"\nPrinting all the remaining element\n";

while(!q.empty()){

cout<<q.front()<<"\n";

q.pop();

}

return 0;

}

Output:

Inserting 1,2,3,4,5 in queue

Is queue empty: 0

Number of items present in Queue: 5

Data at front: 1

Data at front_data: 2

Printing all the remaining element

2

3

4

5

If you have any doubts regarding this then do comment, we will be happy to help you.

Thank You for Reading.