Basic operations of queues in data structures

Queue is a collection of different data types and an important part of the data structure. Elements are inserted and deleted in a specific order. In this tutorial, we will learn about the basic operations of queues.

What is the queue in the data structure?

A queue is a linear data structure, similar to a queue in real life. You've all been in line at school, at the bill counter, or anywhere else, and the first person in will be the first out of the line. Similarly, the queue in the data structure also follows the first-in-first-out principle, which defines first-in, first-out. The element inserted into the queue first will be terminated first compared to the rest of the elements.

The queue has two endpoints and is open to both ends.

• Front - This is the end of the queue at which elements are removed.

• After - This is the end of the queue where the element is inserted.

Can be implemented using one-dimensional arrays, pointers, structures and linked lists. The C library contains various built-in functions that help manage queues, the operations of which occur only in the front-end and back-end.

Syntax for declaring a queue

queue<data type> queue_name

Example

queue<int> q
queue<string> s

Basic queue operations

The most useful operations of queues in C are as follows -

• pop() - It removes the front element of the queue. Syntax -queue_name.pop();

• push() -(): Used to insert elements at the beginning or back of the queue. Syntax -queue_name.push(data_value);

• front() -(): Check or return the element at the front of the queue. Syntax -queue_name.front();

• size() - Used to get the size of the queue. Syntax -queue_name.size();

• empty() - It checks if the queue is empty. Returns a Boolean value based on a condition. Syntax -queue_name.empty();

push() function code.

#include <iostream>
#include<queue>

using namespace std;

int main() {
   queue<int> q; //initializing queue
   q.push(4); //inserting elements into the queue using push() method
   q.push(5);
   q.push(1);
   cout<<"Elements of the Queue are: ";

   while(!q.empty()) {
      cout<<q.front()<<"";  // printing 1st element of the queue
      q.pop();  // removing elements from the queue
   }
   return 0;
}

Output

Elements of the queue are: 451

In the above example, we create a queue q and insert elements into it using the push() function, which inserts all elements to the backend.

Use the empty() function to check whether the queue is empty. If not, the queue will return the front element, and use the pop() function to delete the queue element from the front.

Example

#include <iostream>
#include<queue>

using namespace std;

int main() {
   queue<int> q; //initializing queue
   q.push(4); //inserting elements into the queue using push() method
   q.push(5);
   q.push(1);
   cout<<"Elements of the Queue are: ";

   while(!q.empty()) {
      cout<<q.front()<<""; // printing 1st element of the queue
      q.pop(); // removing elements from the queue
   }
   return 0;
}

Output

size of queue is : 451

Queue empty() function example.

#include <iostream>
#include<queue>

using namespace std;

int main() {
   queue<string> q; //declaring string type of queue
   q.push("cpp"); //inserting elements into the queue using push() method
   q.push("Java");
   q.push("C++");

   if(q.empty()) //using empty() function to return the condition
      cout<<"yes, Queue is empty";
   else
      cout<<"No, queue has elements";

   return 0;
}

Output

No queue has elements

in conclusion

Queue can store integer and string elements. In the data structure, there is an additional queue, called the priority queue, which has priority for all queue elements.

Hope this tutorial can help you understand the meaning of queue in data structure.

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