5 Technical Interview Questions For C# Developers

Preparing for a technical interview can be daunting, especially when you’re aiming to demonstrate your expertise as a C# developer. To help you get ready, we’ve compiled a list of five intermediate-level questions that are commonly asked in technical interviews. By familiarizing yourself with these topics, you’ll be better equipped to tackle challenging questions and impress your interviewers.

Question 1: Explain the difference between abstract class and interface in C#.

Understanding the difference between abstract classes and interfaces is fundamental for C# developers, as both are used to define contracts and provide polymorphic behavior.

Abstract Class:

Can have both abstract methods (without implementation) and non-abstract methods (with implementation). Can contain fields, constructors, and destructors. Can provide default behavior. A class can inherit only one abstract class (single inheritance).

Interface:

Can only have method signatures (methods without implementation), properties, events, and indexers. Cannot contain fields, constructors, or destructors. Cannot provide any default behavior. A class or struct can implement multiple interfaces (multiple inheritance).

Example:

public abstract class Animal
{
    public abstract void MakeSound();
    public void Sleep()
    {
        Console.WriteLine("Sleeping");
    }
}

public interface IFlyable
{
    void Fly();
}

public class Bird : Animal, IFlyable
{
    public override void MakeSound()
    {
        Console.WriteLine("Chirp");
    }
    
    public void Fly()
    {
        Console.WriteLine("Flying");
    }
}

Question 2: What is LINQ and how does it work in C#?

LINQ (Language Integrated Query) is a powerful feature in C# that allows you to query collections in a declarative manner, similar to SQL. LINQ can be used with various data sources such as arrays, collections, XML, and databases.

Key Features:

Provides a consistent query syntax across different data sources. Supports filtering, ordering, and grouping operations. Enables strong typing and IntelliSense support in Visual Studio.

Example:

var numbers = new List<int> { 1, 2, 3, 4, 5 };

var evenNumbers = from num in numbers
                  where num % 2 == 0
                  select num;

foreach (var num in evenNumbers)
{
    Console.WriteLine(num);
}

Question 3: Explain the concept of async and await in C#.

Asynchronous programming is crucial for improving the responsiveness of applications, especially in scenarios involving I/O-bound operations. The async and await keywords in C# simplify writing asynchronous code.

Key Points:

async keyword marks a method as asynchronous. await keyword is used to suspend the execution of an async method until the awaited task completes. The method marked with async must return Task, Task, or void.

Example:

public async Task<string> GetDataAsync()
{
    using (var client = new HttpClient())
    {
        var response = await client.GetStringAsync("https://example.com/data");
        return response;
    }
}

Question 4: What is Dependency Injection and how is it implemented in C#?

Dependency Injection (DI) is a design pattern used to achieve Inversion of Control (IoC) between classes and their dependencies. It enhances code reusability, testability, and maintainability.

Key Concepts:

• Constructor Injection: Dependencies are provided through a class constructor.
• Property Injection: Dependencies are set through public properties.
• Method Injection: Dependencies are passed through method parameters.

Implementing DI in C#:

C# provides built-in support for DI through the Microsoft.Extensions.DependencyInjection namespace.

Example:

public interface IMessageService
{
    void SendMessage(string message);
}

public class EmailService : IMessageService
{
    public void SendMessage(string message)
    {
        Console.WriteLine($"Email sent: {message}");
    }
}

public class Notification
{
    private readonly IMessageService _messageService;

    public Notification(IMessageService messageService)
    {
        _messageService = messageService;
    }

    public void Notify(string message)
    {
        _messageService.SendMessage(message);
    }
}

// Setup DI
var services = new ServiceCollection();
services.AddTransient<IMessageService, EmailService>();
services.AddTransient<Notification>();

var serviceProvider = services.BuildServiceProvider();

// Resolve and use the service
var notification = serviceProvider.GetService<Notification>();
notification.Notify("Hello, Dependency Injection!");

Question 5: How does garbage collection work in C#?

Garbage collection (GC) in C# is an automatic memory management feature that reclaims memory occupied by objects that are no longer in use, preventing memory leaks and optimizing the use of system resources.

Key Concepts:

• Generation 0, 1, and 2: Objects are categorized into three generations. Generation 0 is for short-lived objects, and Generation 2 is for long-lived objects.
• Managed Heap: The area of memory where the GC allocates and deallocates memory.
• GC Roots: Objects referenced directly from application roots, such as static fields and local variables, are considered alive.

How GC Works:

1. Mark Phase: GC identifies which objects are still reachable (alive).
2. Sweep Phase: GC reclaims memory occupied by unreachable objects.
3. Compacting Phase: GC compacts the heap to reduce fragmentation.

Example:

class Program
{
    static void Main()
    {
        for (int i = 0; i < 100; i++)
        {
            CreateObject();
        }

        GC.Collect(); // Forces garbage collection
        GC.WaitForPendingFinalizers(); // Waits for finalizers to complete
    }

    static void CreateObject()
    {
        var obj = new object();
        // obj goes out of scope here and becomes eligible for GC
    }
}

Final Thoughts

Being well-prepared for a technical interview involves more than just knowing the right answers. It requires a deep understanding of core concepts and the ability to apply them effectively. These five questions cover important areas in C# development and will help you showcase your skills and knowledge confidently. Good luck with your interview!