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Top C# Interview Questions: Guide and 20+ Examples from IT Pros

Top C# Interview Questions: Guide and 20+ Examples from IT Pros

Maciej Duszyński
Maciej Duszyński
Resume Expert at Zety

The problem with technical interviews is you never know if you should bring your lucky keyboard—

 

Or marker.

 

Not to mention the C# interview questions you’ll be asked are hardly predictable.

 

The good news?

 

We reached out to several C# experts to share their insights, and tell us what C# coding questions they like to ask to aspiring C# developers.

 

So, keep calm and read on.

 

This article will show you:

 

  • 20+ top C# interview questions.
  • Answers to help you ace the C# interview questions.
  • Advice from experienced developers, researchers, and C# experts.
  • How to answer C# coding questions so they’ll call you back.

 

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1

Whys and Wherefores

 

Listen:

 

Before we even look at any C# interview questions, let’s get one thing straight—

 

First, you need to land an interview.

 

How?

 

Start by learning how to make a resume that stands out.

 

You may want to take a look at one of our dedicated IT resume writing guides:

 

 

And remember—

 

To get a job at the best tech companies you need to ace the entire recruitment process, not just the notoriously hard technical interview part.

 

Now, don’t get me wrong:

 

Your coding skills and intelligence are of paramount importance.

 

But so are your character traits, teamwork, critical thinking, and problem-solving skills.

 

Now, without further ado—

 

Let’s dive into some C# programming interview questions.

 

Technical questions aren’t the only ones you’ll be asked during your interview. Learn how to nail all your interview questions from our guide: Common Job Interview Questions & Answers [Top 35 Samples for 2019]

 

2

C# .NET Interview Questions

 

It’s no secret—

 

C# technical interviews usually consist of several stages.

 

Most of the time they start with C# phone interview questions.

 

The questions asked over the phone will be general coding questions, and because of the medium, focus on the more theoretical aspects of C#.

 

Marie Lamonde from DashThis says:

 

“We built a software that helps marketers gather their data and create their reports. So we have many great software developers with C# experience in our team.”

 

At DashThis, the developer in charge of recruiting and interviewing new employees likes to ask the following questions:

 

  1. Do you have any C# experience?

 

“If not, we fall back to non-programming-language-oriented software development questions. Or questions for any other language known by the candidate.

 

For an interview, we are looking for answers that will help us spot a great software developer.

 

And a great software developer is not one who knows every answer Google can give you in seconds, but one who can make good design decision at the right time.”

 

Remember:

 

It’s one thing to talk about the good decisions you made in the past.

 

If you make it to the next stage you will have to demonstrate your decision making skills, possibly sweating in front a whiteboard, being grilled by a panel of recruiters.

 

  1. What are your tips to write great C# code?

 

“The great answers start with: Like (almost) any other language...

 

Detailed answers circle around those: Simple and simpler, short, read like prose, do what it should, comes with great automated unit tests, use C# features to enhanced readability, etc.

 

As a candidate, you should prepare by reading/practising about Clean Code and Clean Architecture. Practice Test-Driven development until you drop, and pair programming with people with that expertise.”

 

In fact—

 

Websites such as interviewing.io have been specifically created to help coders hone their skills before the actual interview takes place.

 

  1. Which C# features do you like most and why?

 

“We're looking to grasp what the candidate really knows about the language and even more how the candidate applies this language to design/write great software.

 

Candidates should prepare by asking themselves every day how to improve their code/design with the language features.”

 

In other words—

 

You can only become a great coder (and ace your C# interview questions along the way) if coding is something you’re truly passionate about.

 

  1. Which C# structure would you use/do to get the fastest large objects manipulation and when/why would you care?

 

“We want to know if the candidate knows some performance tricks, and when he should care about this performance. Premature optimization is mostly a waste of time and a source of complex solutions.”

 

“Candidate should learn the C# language performance tricks and really learn the ups and downs of every one of them.”

 

It stands to logic—

 

The basic C# interview questions to expect in the initial screening stage won’t really require you to do coding.

 

You’re likely to be asked about your past experience, problems you encountered, solutions you arrived at, or business contexts in which you’ve had a chance to apply your C# coding skills, etc.

 

If you’re looking for more, this article gives you a glimpse into some popular C# interview questions and answers.

 

Moving on to on-site C# interview questions.

 

The good news?

 

Most companies allow you to show off your coding ability in a programming language of your choice.

 

If you’re comfortable with C#, ask for C# coding questions.

 

The bad news?

 

You never know what to expect.

 

So—

 

You need to be ready for everything!

 

Even for being asked to do some rather impractical tasks on occasion.

 

You will have heard the story of Max Howell, creator of Homebrew, being rejected by Google for not being able to invert a binary tree.

 

This is exactly why not even a list of 1000+ C# interview questions and answers may prove sufficient to cover all the possible scenarios.

 

So, what do you do?

 

Well—

 

We reached out to several C# experts to pick their brains on what questions they like to challenge candidates with and why.

 

Dzmitry Valadziankou, Lead .NET Developer at ScienceSoft, has shared his experience on interviewing C# developers.

 

“My ground rule for good interview questions is that they should give a candidate the opportunity to go deep with their answers. The examples of such questions are:

 

  1. What will be the output of the following code snippet?

 

interfaceINamed

{

string Name { get;set; }

}

T[] q =new T[100];//where T some type

INamed named = q[10];

named.Name ="bob";

Console.WriteLine(q[10].Name ??"empty");

Console.ReadKey();

 

The output of the code depends on the type of T—whether it’s the Value type or the Ref type. For the Ref type, the answer will be runtime NullRefenceException, for the Value type — null.

 

Going further, the developer may also explain why this output is expected, cover the difference of the Value type and the Ref type as well as boxing/unboxing concepts.

 

For extra credit, I ask them about the location of the Ref type and the Value type arrays (whether it’s stack or heap) and the speed of array element access.

 

  1. List<T> - what is the efficiency of Add method, RemoveAt method: Add – O(1)amortize, RemoveAt – O(n)

 

Surprisingly, many candidates don’t know about data structures efficiency at all. Also, as the name of the class is misleading, it’s often mistaken for a LinkedList.

 

So, if a candidate knows that this is the implementation of a dynamic array, they not just blindly use it but also look what is under the hood.

 

  1. What is the difference between interface and abstract class?

 

Prior to C# 8, the abstract class could have implementation while interfaces couldn’t. In C# 8, the interface can have default implementation (saying this, a candidate shows that they are up to date).

 

Then, I can proceed and ask what they’ll prefer when designing a class library that will be used by millions of developers and why. The answer should be that the abstract class is better as it allows adding a new method without introducing a breaking change.”

 

The next set of questions comes from Somdip Dey, Embedded A.I. Scientist at the University of Essex, UK.

 

Before working as a scientist, Somdip worked as a Software Engineer and Lead Developer using C# for almost 9 years (including his time at Microsoft), and is one of the top contributors at Microsoft TechNet platform with several recognitions such as C# Guru Award or C# Expert.

 

Here’s what he had to say:

 

“Although most interviews tend to be very varied, there are a few questions related to C# and programming, which come up regularly.

 

I found 3 C# interview questions almost always turn up in interviews for software development positions using C#.

 

Here they are:

 

  1. Can you write the FizzBuzz program in C# now?

 

  1. What are interfaces and abstract classes? And what are the differences between them? Can you give me an example?

 

  1. What is LINQ in C#? Have you used it in your previous programs? Give me an example.

 

These three questions are asked in some form or another if not exactly the way they are spelled out here.

 

So, it’s important to prepare answers for these C# interview questions in advance.

 

First off—

 

The question related to FizzBuzz seems relatively easy for some seasoned programmers but the point of asking this during an interview isn’t just to test the candidate’s coding ability.

 

It also tests whether or not the candidate is knowledgeable about using Dictionaries and/or tuples in C#, which could drastically shorten the lines of code written in the program.

 

Now—

 

The question about interfaces and abstract classes tests the candidate’s understanding of the object oriented paradigm.

 

Plus, the examples are to prove whether or not they can implement interfaces and abstract classes in C#.

 

The LINQ question tests the candidate’s competence in one of the most practically used APIs provided in .NET platform to query and retrieve data from different sources since data is center of all application workflow.

 

I was asked about C# interfaces and abstract classes so many times during my numerous interviews with different companies that I practically wrote an article to demystify the concept".

 

If you wish to find out something more about Somdip Dey, here’s an interview with him.

 

Finally—

 

Christine Orchard from Codementor sent us some of the most common C# interview questions that Ed Freitas has identified in a piece he wrote for the Codementor community:

 

  1. What makes your code really object-oriented?

 

  1. What are the fundamental principles of OO programming?

 

  1. What is the this Pointer?

 

  1. What is the OO fundamental idea using C# that allows a data structure to perform operations on its own data?

 

  1. What is Dynamic Dispatch?

 

  1. Why do we still see so much non-OO code written in C# today?

 

  1. How does OO simplify development?

 

  1. How can we use the core concepts of OO in order to make this code easy to maintain and yet still flexible enough to cope with possibly ever-changing requirements?

 

  1. How to avoid the NULL trap?

 

  1. How to move to a State-related Codebase?

 

  1. What is a state-related codebase?

 

If you don’t how to answer these C# advanced interview questions, check out the original article by Ed Freitas.

 

3

What Does This All Mean?

 

It means one thing:

 

If you’re serious about your C# developer career:

 

You’ve got a lot to learn.

 

And then some more.

 

Technical interviews are the stuff legends.

 

Some say they’ve got nothing to do with real life, and while such radical statements are arguable, one thing is certain—

 

They’re notoriously hard and difficult to prepare for.

 

For example, your C# interview questions could just as well include questions about the entire tech stack C# is part of.

 

For example .NET questions, ASP.NET questions, or Entity Framework questions.

 

In fact, the Devskiller Global Technical Hiring & Skills Report 2019 shows that programming languages are often tested with other technologies in their environment.

 

Plus—

 

There’s a whole thriving community of software engineers centered around helping coding newbies test their skills before the actual technical interview takes place. Check out:

 

 

To name only a few.

 

More than that—

 

Some companies, such as Palantir for example, publish their own guides on how to prepare for a technical interview. Google offers guidelines, too.

 

Remember—

 

Code as much as you can.

 

If you run out of ideas for apps, visit HackerRank or TopCoder to just keep coding.

 

Our resume builder (you can create your resume here) will give you tips and examples on how to write your resume summary or any other section. You can easily copy them straight into your resume - it will save you a ton of time.

 

Inside Zety's resume builder you will find tips and examples for your resume.

 

Key Takeaways

 

Here’s a quick recap of all you need to know about C# interview questions:

 

  • C# interview questions are only a part of the entire technical interview.
  • Expect to be asked basic C# interview questions at the early stages of the recruitment process.
  • Your C# coding interview questions will become harder during the on-site interview.
  • You may be asked to write code live with other programmers on a shared screen, or with a marker on a whiteboard, and “think aloud.”
  • The best way to prepare yourself for C# interview questions is to:
    • practice a lot (preferably with other, more experienced developers)
    • keep challenging yourself
    • be an active member of developer communities
    • gain a broad understanding of the entire technological environment, rather than learn how to answer a number of specific questions.

 

Did you like the article? Do you have your own list of C# programming interview questions? Maybe you’d like to share some C# interview questions and answers? Give us a shout out in the comments below! We’d love to hear from you!

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Maciej Duszyński
Maciej Duszyński
Maciej is a career expert with a solid background in the education management industry. Worked with people at all stages of their career paths: from interns to directors to C-suite members, he now helps you find your dream job.

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