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Key C# Interview Questions To Spot The Best Candidate

Ihor Shcherbinin
VP of Recruiting at DistantJob - - - 3 min. to read

Whether you are a business owner or a manager, it’s always tricky to think of the right questions to ask during an interview. Especially when it comes to hiring a C# developer. 

C-sharp is quite new in the coding language scene, but since it got popular most businesses are using it. Here are the core interview questions to screen a C# developer and hire the most skilled candidates for your team. 

What is C# Development? 

C# is a coding language that has the purpose of creating secure and user-friendly applications that run on the .NET Framework. The story of this coding language starts back in 1999 when Anders Hejlsberg built a team to develop “Cool” language, then renamed C#. Consequently, the project was officially released in July 2000 at the Professional Developers Conference.

C# is a hybrid language that combines C and C++. Like Java, it is an object-based language offering multiple features for applications development. Created by Microsoft, C-sharp is a flexible programming language that allows developers to keep greater control when running and developing applications. 

Where Is C# Used?

A C# developer uses this language to create Windows client applications; XML Web services; distributed components; client-server and database applications and more. Besides its wide applications, this language is limited to development projects based on .NET framework.

These are the field where C# is more functional: 

Web Application Development

Even if limited to .NET framework, C# works on different platforms, such as .NET platform, and other open-source networks. 

Windows Applications

Created by Microsoft, C# works best with its applications. It makes the development process smooth, and each feature is built to perform at full extension. In addition, your developer can count on a vast open-source community sharing support and documentation to develop Microsoft applications and programs. 


C# programming language performs very well in the gaming industry. Developers use it to build fan-favorite games. 

Usually, game developers use engines like Unity to build video games. With over 4.5 million registered developers, Unity includes cross-platform integration supporting 25 platforms, of which 10 outlets are in the UE and five CryEngine. In addition, Unity features 15,000+ free and paid to create 3D models; editor extensions; scripts; shaders; materials; audio; animations, and more.

C# integrates features with the Unity engine. This language works on any mobile device or console for mobile developers, especially with a cross-platform technology like Xamarin. 

> Oh, by the way, we’ve put resources on how to screen and hire Xamarin developers here. <

What do C# Developers do?

C# developers build applications with the .NET framework on Windows operating systems. Their primary duties are to write code, develop, and design user interfaces while debugging and maintaining code for clients. 

Sharp developers are trained as full-stack developers, or take a specialization in front-end or back-end coding.

Here is a list of the core skills and responsibilities to consider when hiring a C# developer:

C sharp developer Skills 

  • Proficiency in C#, concurrency patterns in C#, and the .NET framework (specify which version you are using in your project)
  • Familiarity with the Mono framework 
  • Understanding of object-oriented programming and various design and architectural patterns
  • Writing reusable C# libraries
  • Use of Microsoft SQL Server 
  • Experience with web application frameworks, such as Nancy
  • Windows Presentation Framework 
  • Ability to write clean, readable C# code
  • Basic design principles for a scalable application
  • Building database schemas to support business processes
  • Common Language Runtime (CLR), and its limitations
  • Implementation of automated testing platforms and unit tests
  • Code versioning tools such as Git, SVN, and Mercurial

C sharp Developer Roles and Responsibilities

  • Develop C# .NET solutions for the project 
  • Create in-house applications with the .NET framework
  • Debug and maintain the running code
  • Brainstorming and organization of projects on an ongoing basis
  • Documentation and solution for issues related to .NET projects
  • Manage technical risks and issues
  • Teamwork, technical support to stakeholders in the company
  • Report on project statuses to senior team members

Countries With The Best C# Developer

According to the TIOBE Index, C# is the 4th most popular language worldwide. Hiring remotely, you can look in specific countries to find specialized C# developers. Evans Data’s Global Developer Population and Demographic Study highlights the Asia Pacific region and Latin America as the best countries to hire a C# developer. 

In the past few years, Eastern Europe came into the global scene as one of the major areas to hire developers. In Latin America, Mexico has the most specialized developers for the .NET framework and C#, while The Dominican Republic’s developers are highly specialized with .NET architectures. 

Top 10 C# Interview Questions in 2021

Based on the level of experience you need, here are 10 interview questions to guide you during the hiring process and spot the best C# developer for your business. 

C# Junior Interview Questions

1. What are the types of classes in C#?

Class is an entity containing all the properties of its objects and instances as a single unit. 

C# has four types of such classes:

  • Static class: In the static class, the keyword ‘static’ does not allow inheritance. Therefore, you can’t create an object for a static class.

Code Sample: 

static class classname  
  //static data members  
  //static methods  

  • Partial class: here, the keyword ‘partial’ allows members to partially divide or share source (.cs) files.
  • Abstract class: In these classes, you cannot create objects and they work on the OOPS concept of abstraction to extract essential details and hide the unessential ones.
  • Sealed class: Sealed classes cannot be inherited. The keyword sealed restricts access to users to inherit that class.

sealed class InterviewBit
   // data members
   // methods

2. What is garbage collection in C#?

Garbage collection is the process of freeing up memory stored by unwanted objects. When you create a class object, automatically some memory space allocates in the object in the heap memory. After that, you perform the actions on the object, and the memory space is a waste to eliminate. 

In short, the garbage collection happens in three cases:

  • The occupied memory by the objects exceeds the pre-set threshold value.
  • You call the garbage collection method. 
  • Low physical memory.

3. What are the differences between ref and out keywords?

C# ref keywords pass arguments by reference rather than not value. To use the ‘ref’ keyword, you need to explicitly mention ‘ref’. 

void Method(ref int refArgument)
   refArgument = refArgument + 10;
int number = 1;
Method(ref number);
// Output: 11

C# out keywords pass arguments within methods and functions. 

‘out’ keyword is used to pass arguments as a reference to return multiple values. Although it is the same as the ref keyword, it needs an initialization before passing. Here, the out and ref keywords are useful to return a value in the same variables as an argument. 

public static string GetNextFeature(ref int id)  
   string returnText = "Next-" + id.ToString();  
   id += 1;  
   return returnText;  
public static string GetNextFeature(out int id)  
   id = 1;  
   string returnText = "Next-" + id.ToString();  
   return returnText;  

4. What are extension methods in C#?

Extension methods add new methods (usually static) to the existing ones. At times, when you want to add methods to an existing class without the rights to modify the class, you can create a new static class containing the new methods. After that, bind this class with the existing one and the methods will be added to the existing one.

// C# program to illustrate the concept
// of the extension methods
using System;
namespace ExtensionMethod {
static class NewMethodClass {
   // Method 4
   public static void M4(this Scaler s)
       Console.WriteLine("Method Name: M4");
   // Method 5
   public static void M5(this Scaler s, string str)
// Now we create a new class in which
// Scaler class access all the five methods
public class IB {
   // Main Method
   public static void Main(string[] args)
       Scaler s = new Scaler();
       s.M5("Method Name: M5");

5. What is the difference between an Array and ArrayList in C#?

An array is a collection of similar variables clubbed together under one common name. On the other hand, an ArrayList is a collection of objects that can be indexed individually. Therefore, you can access a number of features like dynamic memory allocation, adding, searching, and sorting items in the ArrayList. 

  • When declaring an array the size of the items is fixed therefore, the memory allocation is fixed. But with ArrayList, it can be increased or decreased dynamically.
  • Array belongs to system.array namespace while ArrayList belongs to the system.collection namespace.
  • All items in an array are of the same datatype while all the items in an ArrayList can be of the same or different data types.
  • While arrays cannot accept null, ArrayList can accept null values.

For example:

// C# program to illustrate the ArrayList
using System;
using System.Collections;
class IB {
   // Main Method
   public static void Main(string[] args)
       // Create a list of strings
       ArrayList al = new ArrayList();
       // Iterate list element using foreach loop
       foreach(var names in al)

C# Senior Interview Questions

6. What are partial classes in C#?

Partial classes implement the functionality of a single class into multiple files. These multiple files are combined into one during compile time. It’s possible to create this class using the partial keyword. 

public partial Clas_name  
       // code

You can easily split the functionalities of methods, interfaces, or structures into multiple files, and even add nested partial classes. 

7. What is the difference between late binding and early binding in C#?

Late binding and early binding are examples of one of the primary concepts of OOPS: Polymorphism

For example, one function calculateBill() will calculate bills of premium customers, basic customers, and semi-premium customers based on their policies differently. The calculation for all the customer objects is done differently using the same function which is called polymorphism. 

When an object is assigned to an object variable in C#, the .NET framework performs the binding. 

Meanwhile, the binding function happens at compile-time, it is called early binding. It investigates and checks the methods and properties of static objects. With early binding, the number of run-time errors decreases substantially and it executes pretty quickly. 

And if the binding happens at runtime, it is called late binding. The latter happens when the objects are dynamic (decided based on the data they hold) at run-time. It is slower as it looks through during run-time.

8. Difference between the Equality Operator (==) and Equals() Method in C#?

Although both are used to compare two objects by value, still they both are used differently.

For example:  

int x = 10;
int y = 10;
Console.WriteLine( x == y);

Equality operator (==) is a reference type which means that if equality operator is used, it will return true only if both the references point to the same object.  

Equals() method: Equals method is used to compare the values carried by the objects. int x=10, int y=10. If x==y is compared then, the values carried by x and y are compared which is equal and therefore they return true. 

Equality operator: Compares by reference

Equals(): Compares by value 

9. What are the different ways in which a method can be Overloaded in C#?

Overloading means when a method has the same name but carries different values to use in a different context. Only the main() method cannot be overloaded.

In order to overload methods in C#, 

  • Transform the number of parameters in a method
  • Change the order of parameters in a method
  • Use different data types for parameters

In these ways, you can overload a method multiple times.  

For example:

public class Area {
   public double area(double x) {
       double area = x * x;
       return area;
   public double area(double a, double b) {
       double area = a * b;
       return area;

Here, the method Area is used twice. In the first declaration, one argument is used and the second one uses two arguments. Using different parameters in the same method, we were able to overload the method area().

10. What is the difference between constant and readonly in C#?

A const keyword in C# is used to declare a constant field throughout the program. That means once a variable has been declared const, its value cannot be changed throughout the program. 

In C#, a constant is a number, string, null reference, or boolean values. 

For example:

class IB {
   // Constant fields
   public const int xvar = 20;
   public const string str = "InterviewBit";
   // Main method
   static public void Main()
       // Display the value of Constant fields
       Console.WriteLine("The value of xvar: {0}", xvar);
       Console.WriteLine("The value of str: {0}", str);
The value of xvar is 20.
The value of string is Interview Bit

On the other hand, with readonly keyword, you can assign the variable only when it is declared or in a constructor of the same class in which it is declared. 

For example:

public readonly int xvar1;
   public readonly int yvar2;
   // Values of the readonly 
   // variables are assigned
   // Using constructor
   public IB(int b, int c)
       xvar1 = b;
       yvar2 = c;
       Console.WriteLine("The value of xvar1 {0}, "+
                       "and yvar2 {1}", xvar1, yvar2);
   // Main method
   static public void Main()
     IB obj1 = new IB(50, 60);

The value of xvar1 is 50, and yvar2 is 60

Constants are static by default while readonly should have a value assigned when the constructor is declared. They can be declared within functions while readonly modifiers can be used with reference types.  

It’s Up To You

Hiring a C# developer is a tedious process, and isolating the skills you need to make the right questions is the most challenging part but hopefully, we made it easier for you. Now you know what to look for and what interview questions to ask to spot the best candidate for your team. Want to know how to hire a remote developer for your project? Check our guide or give us a call; our team can help you. We have more than a decade of experience in headhunting the best developers from all over the world.

Ihor Shcherbinin

Ihor, is the VP of Recruiting at DistantJob. He specializes in sourcing and placing top remote developers for North American companies. His expertise covers the entire recruiting cycle, from pinpointing job needs to finalizing hires. Known for his skill in remote staffing solutions and offshore team integration, Ihor excels in matching the best tech talents with U.S. organizations. His approach to virtual developer hiring is marked by insightful candidate selection and strategic offer negotiation, ensuring the right fit for every role.

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