C# Queue Class (original) (raw)

Last Updated : 31 Jan, 2025

In C#, the **Queue class is the part of the **System.Collections.Generic namespace and represent a first-in-first-out (FIFO) collection of objects. When we add an item to the list, it is called **enqueue, and when we remove an item, it is called **dequeue.

• **Enqueue adds an element to the end of the Queue.
• **Dequeue removes the oldest element from the start of the Queue.
• **Peek returns the oldest element that is at the start of the Queue but does not remove it from the Queue.
• The **capacity of a Queue is the number of elements the Queue can hold.
• As elements are added to a Queue, the capacity is automatically increased as required by reallocating the internal array.
• Queue accepts **null as a valid value for reference types and allows duplicate elements.

**Example: This example, demonstrates how to create a queue, add different elements to it using the enqueue() Method, and then display the elements using for-each loop.

C# `

// C# program to demonstrates the working of queue using System; using System.Collections;

public class Geeks { static public void Main() {

    // Create a queue
    // Using Queue class
    Queue q = new Queue();

    // Adding elements in Queue
    // Using Enqueue() method
    q.Enqueue("GFG");
    q.Enqueue(1);
    q.Enqueue(10);
    q.Enqueue(null);
    q.Enqueue(2.4);
    q.Enqueue("Geeks123");

    // Accessing the elements
    // of q Queue
    // Using foreach loop
    foreach(var i in q) { 
      Console.WriteLine(i); 
    }
}

}

`

Output

GFG 1 10

2.4 Geeks123

Declaration of Queue Class

In C#, the Queue is a **generic collection, meaning it can hold elements of a specific type. T is the type of elements the queue will hold

Queue q = new Queue();

Constructors

The Queue class provides four constructor which are listed below in the table:

**Example: This example demonstrates the total number of elements present in the queue.

C# `

// C# program to count the number // of elements present in the queue using System; using System.Collections;

class Geeks {

public static void Main()
{

    // Creating a Queue
    Queue q = new Queue();

    // Inserting the elements into the Queue
    q.Enqueue("one");
    q.Enqueue("two");
    q.Enqueue("three");
    q.Enqueue("four");
    q.Enqueue("five");

    // Displaying the count of elements
    // contained in the Queue
    Console.Write(
        "Total number of elements in the Queue are : ");

    Console.WriteLine(q.Count);
}

}

`

Output

Total number of elements in the Queue are : 5

Properties

The Queue class provides several properties to access its state.

**Example: This example demonstrates how to use the SyncRoot property of a Queue to ensure thread safety.

C# `

// C# program to illustrate the // use of SyncRoot property of // the Queue using System; using System.Threading; using System.Collections;

namespace sync_root {

class Geeks {

// Main Method
static void Main(string[] args)
{

    // Declaring an Queue
    Queue q = new Queue();

    // Adding elements to Queue
    q.Enqueue(1);
    q.Enqueue(2);
    q.Enqueue(3);
    q.Enqueue(4);
    q.Enqueue(5);

    // Using the SyncRoot property
    lock(q.SyncRoot)
    {
        // foreach loop to display
        // the elements in q1
        foreach(Object i in q) Console.WriteLine(i);
    }
}

} }

`

Methods

**Example: This example demonstrates that the specific element is present in the Queue using the Contains() method.

C# `

// C# Program to check if the specified // element is present in the queue or not using System; using System.Collections;

class Geeks {

public static void Main()
{

    // Creating a Queue
    Queue q = new Queue();

    // Inserting the elements into the Queue
    q.Enqueue(5);
    q.Enqueue(10);
    q.Enqueue(15);
    q.Enqueue(20);
    q.Enqueue(25);

    // Checking whether the element is
    // present in the Queue or not
    Console.WriteLine("The queue contains 7 ? :"
                      + q.Contains(7));
    Console.WriteLine("The queue contains 10 ? :"
                      + q.Contains(10));
}

}

`

Output

The queue contains 7 ? :False The queue contains 10 ? :True

**Example: This example demonstrates how to convert a Queue to an object array using ToArray() method.

C# `

// C# Program to Convert Queue to array using System; using System.Collections;

class Geeks {

public static void Main()
{

    // Creating a Queue  
    Queue q = new Queue();

    // Inserting the elements into the Queue 
    q.Enqueue("Geeks");
    q.Enqueue("for");
    q.Enqueue("Geeks");

    // Converting the Queue 
    // into object array 
    Object[] arr = q.ToArray();

    // Displaying the elements in array 
    foreach(Object i in arr)
    {
        Console.WriteLine(i);
    }
}

}

`