Queue and Stack behavior in C Sharp (C#)

Introduction

Queues and stacks help us organize data in a specific order so we can add and remove items easily. They work like real-life lines or piles.

When you want to process tasks in the order they arrive, like people waiting in line at a store (Queue).

When you want to reverse the order of items, like stacking plates and taking the top one first (Stack).

When you need to undo actions, like pressing undo in a text editor (Stack).

When you want to handle requests in the order they come, like print jobs sent to a printer (Queue).

When you want to explore things step-by-step and backtrack, like navigating a maze (Stack).

Syntax

C Sharp (C#)

using System;
using System.Collections.Generic;

public class QueueAndStackDemo
{
    public static void Main()
    {
        // Queue example
        Queue<int> numberQueue = new Queue<int>();
        numberQueue.Enqueue(1); // Add to end
        numberQueue.Enqueue(2);
        int firstInQueue = numberQueue.Dequeue(); // Remove from front

        // Stack example
        Stack<int> numberStack = new Stack<int>();
        numberStack.Push(1); // Add to top
        numberStack.Push(2);
        int topOfStack = numberStack.Pop(); // Remove from top
    }
}

Queue uses FIFO (First In First Out) order: first added is first removed.

Stack uses LIFO (Last In First Out) order: last added is first removed.

Examples

Queue with strings. Items come out in the order they were added.

C Sharp (C#)

Queue<string> tasks = new Queue<string>();
tasks.Enqueue("Task1");
tasks.Enqueue("Task2");
string nextTask = tasks.Dequeue();

Stack with strings. Items come out in reverse order of adding.

C Sharp (C#)

Stack<string> history = new Stack<string>();
history.Push("Page1");
history.Push("Page2");
string lastPage = history.Pop();

Trying to remove from an empty queue causes an error.

C Sharp (C#)

Queue<int> emptyQueue = new Queue<int>();
// Dequeue on empty queue throws InvalidOperationException

Stack with one item. Pop removes that item, then stack is empty.

C Sharp (C#)

Stack<int> singleStack = new Stack<int>();
singleStack.Push(10);
int onlyItem = singleStack.Pop();

Sample Program

This program shows how a queue and a stack work. It adds items, shows them, removes one, then shows the remaining items.

C Sharp (C#)

using System;
using System.Collections.Generic;

public class QueueAndStackBehavior
{
    public static void Main()
    {
        // Create a queue and add items
        Queue<string> customerQueue = new Queue<string>();
        customerQueue.Enqueue("Alice");
        customerQueue.Enqueue("Bob");
        customerQueue.Enqueue("Charlie");

        Console.WriteLine("Queue before dequeue:");
        foreach (string customer in customerQueue)
        {
            Console.WriteLine(customer);
        }

        // Remove one item from queue
        string servedCustomer = customerQueue.Dequeue();
        Console.WriteLine($"\nServed customer: {servedCustomer}");

        Console.WriteLine("Queue after dequeue:");
        foreach (string customer in customerQueue)
        {
            Console.WriteLine(customer);
        }

        // Create a stack and add items
        Stack<string> bookStack = new Stack<string>();
        bookStack.Push("Book1");
        bookStack.Push("Book2");
        bookStack.Push("Book3");

        Console.WriteLine("\nStack before pop:");
        foreach (string book in bookStack)
        {
            Console.WriteLine(book);
        }

        // Remove one item from stack
        string topBook = bookStack.Pop();
        Console.WriteLine($"\nRemoved from stack: {topBook}");

        Console.WriteLine("Stack after pop:");
        foreach (string book in bookStack)
        {
            Console.WriteLine(book);
        }
    }
}

Important Notes

Queue operations Enqueue and Dequeue run in O(1) time.

Stack operations Push and Pop run in O(1) time.

Trying to Dequeue or Pop from an empty collection throws an exception; always check if empty first.

Use Queue when order matters and you want to process oldest items first.

Use Stack when you want to reverse order or track recent items first.

Summary

Queue follows FIFO: first added, first removed.

Stack follows LIFO: last added, first removed.

Both are useful for organizing data in different real-life scenarios.