Queue.Dequeue Method in C#

The Queue.Dequeue() method in C# is used to remove and return the object at the beginning of the Queue. This method follows the FIFO (First In, First Out) principle, where the first element added to the queue is the first one to be removed.

Syntax

Following is the syntax for the Dequeue() method −

public T Dequeue();

Return Value

The method returns the object that is removed from the beginning of the Queue. If the queue is empty, it throws an InvalidOperationException.

Using Dequeue() to Remove Elements

Example

using System;
using System.Collections.Generic;

public class Demo {
   public static void Main() {
      Queue<string> queue = new Queue<string>();
      queue.Enqueue("A");
      queue.Enqueue("B");
      queue.Enqueue("C");
      queue.Enqueue("D");
      queue.Enqueue("E");
      queue.Enqueue("F");
      queue.Enqueue("G");
      
      Console.WriteLine("Count of elements = " + queue.Count);
      Console.WriteLine("Element at the beginning of queue = " + queue.Peek());
      
      // Remove three elements and show which ones were removed
      Console.WriteLine("Removed: " + queue.Dequeue());
      Console.WriteLine("Removed: " + queue.Dequeue());
      Console.WriteLine("Removed: " + queue.Dequeue());
      
      Console.WriteLine("Count of elements = " + queue.Count);
   }
}

The output of the above code is −

Count of elements = 7
Element at the beginning of queue = A
Removed: A
Removed: B
Removed: C
Count of elements = 4

Using Dequeue() with Queue Processing

Example

using System;
using System.Collections.Generic;

public class Demo {
   public static void Main() {
      Queue<string> queue = new Queue<string>();
      queue.Enqueue("Gary");
      queue.Enqueue("Jack");
      queue.Enqueue("Ryan");
      queue.Enqueue("Kevin");
      queue.Enqueue("Mark");
      queue.Enqueue("Alice");
      
      Console.WriteLine("Count of elements = " + queue.Count);
      Console.WriteLine("Original Queue:");
      foreach(string i in queue) {
         Console.WriteLine(i);
      }
      
      // Process first two elements
      string first = queue.Dequeue();
      string second = queue.Dequeue();
      Console.WriteLine("\nProcessed: " + first + " and " + second);
      
      Console.WriteLine("\nUpdated Queue:");
      foreach(string i in queue) {
         Console.WriteLine(i);
      }
      Console.WriteLine("Count of elements (updated) = " + queue.Count);
   }
}

The output of the above code is −

Count of elements = 6
Original Queue:
Gary
Jack
Ryan
Kevin
Mark
Alice

Processed: Gary and Jack

Updated Queue:
Ryan
Kevin
Mark
Alice
Count of elements (updated) = 4

Exception Handling with Empty Queue

Example

using System;
using System.Collections.Generic;

public class Demo {
   public static void Main() {
      Queue<int> queue = new Queue<int>();
      
      // Safe dequeue using Count check
      if (queue.Count > 0) {
         Console.WriteLine("Dequeued: " + queue.Dequeue());
      } else {
         Console.WriteLine("Queue is empty - cannot dequeue");
      }
      
      // Add elements and then dequeue safely
      queue.Enqueue(10);
      queue.Enqueue(20);
      
      while (queue.Count > 0) {
         Console.WriteLine("Dequeued: " + queue.Dequeue());
      }
      
      Console.WriteLine("Queue is now empty. Count: " + queue.Count);
   }
}

The output of the above code is −

Queue is empty - cannot dequeue
Dequeued: 10
Dequeued: 20
Queue is now empty. Count: 0

Conclusion

The Queue.Dequeue() method removes and returns the element at the front of the queue, maintaining FIFO order. Always check if the queue contains elements using Count property before calling Dequeue() to avoid exceptions when the queue is empty.