Remove all objects from the Queue in C#

To remove all objects from a Queue in C#, use the Clear() method. This method removes all elements from the Queue and resets its count to zero. The Queue<T> class provides this built-in method for efficient bulk removal of all elements.

Syntax

Following is the syntax for the Clear() −

queue.Clear();

Where queue is the Queue object from which all elements will be removed.

Using Clear() Method

Example 1

The following example demonstrates clearing a Queue containing string elements −

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("Jack");
      queue.Enqueue("Ryan");
      queue.Enqueue("Kevin");
      
      Console.WriteLine("Count of elements = " + queue.Count);
      queue.Clear();
      Console.WriteLine("Count of elements (after Clear) = " + queue.Count);
   }
}

The output of the above code is −

Count of elements = 8
Count of elements (after Clear) = 0

Example 2

Here's another example showing the Clear operation with a different set of elements −

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");
      
      Console.WriteLine("Count of elements = " + queue.Count);
      queue.Clear();
      Console.WriteLine("Count of elements (after Clear) = " + queue.Count);
   }
}

The output of the above code is −

Count of elements = 5
Count of elements (after Clear) = 0

Working with Different Data Types

Example 3

The Clear() method works with Queues of any data type. Here's an example with integers −

using System;
using System.Collections.Generic;

public class Demo {
   public static void Main() {
      Queue<int> numberQueue = new Queue<int>();
      numberQueue.Enqueue(10);
      numberQueue.Enqueue(20);
      numberQueue.Enqueue(30);
      numberQueue.Enqueue(40);
      
      Console.WriteLine("Initial count: " + numberQueue.Count);
      Console.WriteLine("Queue contains elements: " + (numberQueue.Count > 0));
      
      numberQueue.Clear();
      
      Console.WriteLine("Count after Clear(): " + numberQueue.Count);
      Console.WriteLine("Queue is empty: " + (numberQueue.Count == 0));
   }
}

The output of the above code is −

Initial count: 4
Queue contains elements: True
Count after Clear(): 0
Queue is empty: True

Key Points

• The Clear() method has O(n) time complexity where n is the number of elements.

• After calling Clear(), the Queue's Count property returns 0.

• The method does not return any value (void method).

• It's safe to call Clear() on an already empty Queue.

Conclusion

The Clear() method is the most efficient way to remove all elements from a Queue in C#. It immediately empties the Queue and resets its count to zero, making it ready for new elements to be enqueued.