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An Example of Creating and Using Stack and Queue in C#

Author:

I am a software engineer. I have been working with C++, MFC, and .net technologies for 15 years. I like video games and reading books.

1. Introduction

Stack and Queue both are collection classes supported by the dot net framework. Queue operates on the “First in First Out (FIFO)” principle. Stack operates on the “Last in First out (LIFO)” principle. That is; when you remove an item from the Queue, the first added item will be removed first. In the case of the stack it is in the reverse order, which means, the item added Last removed first.

To use Stack and Queue on your application first, include the namespace “System.Collection”.

//000: Use the Collection namespace to 
//have access to collection classes
using System.Collections;

2. Using C# Queue Class

We use the Queue and stack both in our Static Main method. First, let us go with Queue.

1) First, we create a Queue and store 5 integers in it. Then we use Queue class’s Enqueue() function to add an element at the back of the Q. In our example, both Queue and stack will be placed Static Main method. First, let us go with Queue.

//===============> A. Queue  <==================
Console.WriteLine("===============> A. Queue" + 
    "  <==================");
//A_001: Create a Queue and populate it.
Queue Q = new Queue();

//A_002: populate 5 Integers to it. 
//Enqueue adds an element to the Queue and the End.
for (int i=0; i<5; i++)
	Q.Enqueue(i+1);

2) We write a function to display all the elements in the Queue. The function takes the IEnumerable interface as a parameter. This means, the function expects an object which implements the IEnumerable interface. Then, the function walks through the collection object and displays each element in it.

//001: Display the passed in collection. 
//Note the collection Stack, Queue, 
//Hash all implements IEnumerable
public static void DisplayContent
    (string collection_name, 
    IEnumerable collection )
{
    Console.Write("Content of {0}: ", collection_name );
    foreach(int item in collection)
        Console.Write(item + ", " );
    Console.WriteLine();
}

3) The Peek() method will return the first item in the Queue. That is; it will get the element first added (One that is there in the Front). However, Peek() method will not remove the item from the Queue. But, the Dequeue() will take the item from the front and removes it. The usage of Peek() and Dequeue() is shown in the below Code:

//A_003: Show the Queue Content
DisplayContent("Queue", Q );

//A_004: Return the Object at the begining 
//of the Queue
Console.WriteLine("First element: {0}", Q.Peek());

//A_005: Show the Queue Content.
DisplayContent("Queue", Q );

//A_006: Remove the First two element from the Queue. 
//Note: The first two entries added will be removed
Console.WriteLine("First Removed Element: {0}" , 
    Q.Dequeue());
Console.WriteLine("Second Removed Element: {0}" , 
    Q.Dequeue());

//A_007: Show the Queue Content
DisplayContent("Queue", Q );

Output of executing the above is given here below:

C Sharp Queue Example

C Sharp Queue Example

3. Using C# Stack Class

The code we see below is copy pasted from Queue and changed for Stack. When we add an element using push function, it will be added in the Top. When you remove an item using pop, it will be removed from the Top of the Stack. Hence, the item added last will be removed first. The below code shows the usage of Stack:

//===============> B. Stack  <==================
Console.WriteLine(
    "===============> B. Stack  <==================");
//B_001: Create a Stack and populate it.
Stack S = new Stack();

//B_002: populate 5 Integers to it. Push adds an 
//element to the Stack at the front that is top
for (int i=0; i<5; i++)
	S.Push(i+1);

//B_003: Show the Stack Content
DisplayContent("Stack", S );

//B_004: Return the Object at the begining of the Stack
Console.WriteLine("First element: {0}", S.Peek());

//B_005: Show the Stack Content.
DisplayContent("Stack", S );

//B_006: Remove the First two element from the Stack. 
//Note: The Last two entries added will be removed
Console.WriteLine("First Removed Element: {0}" , 
    S.Pop());
Console.WriteLine("Second Removed Element: {0}" , 
    S.Pop());

//B_007: Show the Queue Content
DisplayContent("Stack", S );

Output of executing the Stack Example is shown below:

C# Stack Example: Output

C# Stack Example: Output

Pictorial representation of Stack and Queue used in this Example


Stack and Queue

Stack and Queue

4. Complete C-Sharp Code Example of Stack and Queue

using System;
//000: Use the Collection namespace to 
//have access to collection classes
using System.Collections;

namespace CollectionClasses
{
	class CollectionsExp
	{
		[STAThread]
		static void Main(string[] args)
		{
            //===============> A. Queue  <==================
            Console.WriteLine("===============> A. Queue" + 
                "  <==================");
            //A_001: Create a Queue and populate it.
            Queue Q = new Queue();

            //A_002: populate 5 Integers to it. 
            //Enqueue adds an element to the Queue and the End.
            for (int i=0; i<5; i++)
	            Q.Enqueue(i+1);

            //A_003: Show the Queue Content
            DisplayContent("Queue", Q );

            //A_004: Return the Object at the begining 
            //of the Queue
            Console.WriteLine("First element: {0}", Q.Peek());

            //A_005: Show the Queue Content.
            DisplayContent("Queue", Q );

            //A_006: Remove the First two element from the Queue. 
            //Note: The first two entries added will be removed
            Console.WriteLine("First Removed Element: {0}" , 
                Q.Dequeue());
            Console.WriteLine("Second Removed Element: {0}" , 
                Q.Dequeue());

            //A_007: Show the Queue Content
            DisplayContent("Queue", Q );


            //===============> B. Stack  <==================
            Console.WriteLine(
                "===============> B. Stack  <==================");
            //B_001: Create a Stack and populate it.
            Stack S = new Stack();

            //B_002: populate 5 Integers to it. Push adds an 
            //element to the Stack at the front that is top
            for (int i=0; i<5; i++)
	            S.Push(i+1);

            //B_003: Show the Stack Content
            DisplayContent("Stack", S );

            //B_004: Return the Object at the begining of the Stack
            Console.WriteLine("First element: {0}", S.Peek());

            //B_005: Show the Stack Content.
            DisplayContent("Stack", S );

            //B_006: Remove the First two element from the Stack. 
            //Note: The Last two entries added will be removed
            Console.WriteLine("First Removed Element: {0}" , 
                S.Pop());
            Console.WriteLine("Second Removed Element: {0}" , 
                S.Pop());

            //B_007: Show the Queue Content
            DisplayContent("Stack", S );

		}

        //001: Display the passed in collection. 
        //Note the collection Stack, Queue, 
        //Hash all implements IEnumerable
        public static void DisplayContent
            (string collection_name, 
            IEnumerable collection )
        {
            Console.Write("Content of {0}: ", collection_name );
            foreach(int item in collection)
                Console.Write(item + ", " );
            Console.WriteLine();
        }
	}
}

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