Top C# Coding Interview Questions and Answers You Need to Prepare

Released in 2002 by Microsoft, C# is a programming language widely used in web development. Owing to its significance in the tech field, C# coding interview questions are highly valued during technical interviews.

Because there are so many questions to sort through, practicing the most important C# coding interview questions can be difficult for freshers and experienced professionals. In this article, we'll look at the top questions you should practice to ace the C# coding interview.

What is C# and What are its Features?

Pronounced ‘see sharp,’ C# is an object-oriented programming (OOP) language. It was released in 2002 by Microsoft and standardized by ISO and ECMA to be used on the .NET platform. The latest version of the language is C# 6.0.

The primary features of C# are:

• It’s a simple, modern, purely object-oriented programming language.
• It includes a feature known as versioning that helps create new versions of module work using the existing version.
• It’s several times faster than BASIC

Basic C# Coding Interview Questions And Answers

‍

‍

Q1. How would you explain the concept of encapsulation in C#?

Encapsulation in C# is a fundamental object-oriented programming concept that involves bundling data (attributes) and methods (functions) that operate on that data into a single unit called a class. This unit controls access to its internal data, allowing it to be hidden from external code. Encapsulation promotes data integrity and security by enforcing controlled interactions with the class through well-defined interfaces.

Q2. Explain inheritance in C#.

A class can receive traits and behaviors through inheritance from another class (also known as a superclass or base class). The operator can be used to accomplish this in C#. In the subclass, inherited members can be modified or replaced.

Q3. What distinguishes C#'s inheritance and composition clauses? What would make you choose one over the other?

Inheritance is an "is-a" relationship that allows one class to use the properties and methods of another class. Contrarily, composition is a "has-a" relationship in which an instance of one class is contained by another. When you want to give a new class the traits of an existing one, inheritance is frequently used.

In contrast, the composition is used to build complex obj builds complex objects by combining simpler ones. You might prefer inheritance when promoting code reuse, etc. by combining simpler ones. You might prefer inheritance when promoting code reuse, but composition is often more flexible and can avoid the issues of tight coupling that can arise with inheritance.

Also read: Top Object-oriented Programming Interview Questions in C# and C++

C# Coding Interview Questions On Value Types vs Reference Types

These C# coding interview questions primarily focus on concepts of value and reference types. C# stores value types directly in the stack; that is, each variable has a copy of the data. This is commonly used for basic types, such as int, float, or any struct, amongst others. For reference types, the data lives in the heap but its memory address is stored in the stack.

Such types include class, string, and arrays. Reference types allow for multiple variables to hold references to the same data, so change in any variable causes all references to that data to be affected. On the other hand, value types work independently after assignment.

Q4. What are value types and reference types in C#? Can you provide examples of each and describe their behaviours?

In C#, reference types store a reference to the data on the heap while value types store their actual data on the stack. Small, immutable data is stored in value types, which include primitive types like int, float, and char. Reference types, like classes and interfaces, store pointers to the actual data, enabling more intricate object hierarchies and dynamic memory allocation.

Q5. And what happens if you add a reference type variable to another? Does the same thing with value types?

When you assign one reference type variable to another, both variables point to the same object (in memory). Thus, modifications to one variable will also be applied to the other. Alternatively, the result of assigning one value type to another will create a different (copy) value, and changes made in the second type will not reflect on the first.

Additional C# Coding Interview Questions on Value vs Reference Types

• What is the difference between a nullable value type and reference type that can be null?
• When would you use struct (value type) versus class (reference type) in C#?
• How does garbage collection affect memory management in the case of reference types?
• How is equality comparison handled for value types and reference types?
• What are some potential problems that occur with mutable reference types and how do immutable values avoid them
• Explain some of the pros and cons of using value types in performance-sensitive C# applications.
• How does "pass-by-reference" affect the behavior of value and reference types?
• What are some best practices for making good use of value types and reference types to optimize performance in C# applications?

C# Coding Interview Questions On Delegates and Events

Q6. Explain delegates and their usage in C#.

This is one of the most commonly asked C# interview questions. Delegates are function pointers that allow you to pass methods as arguments to other methods. They are commonly used in event handling, callbacks, and creating custom events. Delegates provide a way to achieve loose coupling between components in an application.

Q7. What are events in C#, and how are they different from delegates?

Events are a higher-level concept built on top of delegates. They provide a mechanism for one class (the publisher) to notify other classes (subscribers) when a specific action or event occurs. Events encapsulate delegates and restrict external code from directly invoking them.

C# Coding Interview Questions On Exception Handling

Q8. Describe the C# system for handling exceptions. Which standard exception-handling constructs should you use and when?

You can expect some kind of C# coding interview questions on exception handling.

It involves trying, catching, and finally, blocks in C#. The code that might cause an exception is in the try block, and the catch block takes care of it if it does. The last block makes sure that some code is run whether or not an exception is thrown. You should use exception handling to gracefully handle unexpected errors and maintain the stability of your application.

C# Coding Interview Questions On LINQ (Language Integrated Query)

Q9. What is LINQ, and how does it simplify data manipulation in C#? Can you provide a LINQ query example for a collection?

LINQ (Language Integrated Query) is a powerful feature in C# that simplifies data manipulation by allowing developers to query and manipulate data from various sources, like collections, databases, and XML, using a uniform syntax. It enhances code readability and reduces the need for complex loops.

Example LINQ query for a collection:

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

var evenNumbers = from num in numbers

                 where num % 2 == 0

                 select num;

// 'evenNumbers' now contains [2, 4]

This LINQ query filters even numbers from the 'numbers' collection, making data manipulation concise and readable.

C# Coding Interview Questions On Asynchronous Programming

Q10. Explain what do you mean by asynchronous programming using C# keywords async and await. Mention the advantages of asynchronous programming, and when would you use it?

The "async" and "await" keywords are used in asynchronous programming in C# to enable non-blocking operations. It allows tasks to run concurrently, enhancing responsiveness in applications. Benefits include improved performance, as it prevents blocking the main thread, making it ideal for I/O-bound and CPU-bound operations. It's useful when dealing with long-running tasks, network requests, or parallel processing.

C# Coding Interview Questions On Dependency Injection

Q11. How would you write C# code while making it simpler to test and maintain using dependency injection?

In C#, simplify testability and maintenance by implementing Dependency Injection (DI). Create interfaces for dependencies, inject them into classes via constructors, and configure a DI container. This decouples components, eases unit testing with mock objects, and promotes code flexibility. Updates and maintenance become easier due to reduced coupling, enhancing code readability and maintainability.

C# Coding Interview Questions On Multithreading

Q12. How do you create and manage threads in C#?

Multithreading is supported by C#'s System.namespace for threads. Using the Thread class or higher-level abstractions like Task, you can create and manage threads. Proper synchronization mechanisms like locks are essential to prevent race conditions and ensure thread safety.

C# Coding Interview Questions On Memory Management and Garbage Collection

Q13. What steps are involved in garbage collection in C#?

A garbage collector automatically manages memory in C#. The garbage collector tracks and identifies objects that are no longer reachable and releases their memory. Developers can also implement the IDisposable pattern to release unmanaged resources explicitly.

C# Coding Interview Questions On Features and Language Specifics

Q14. What distinguishes C# var and explicit type declarations from one another?

The var keyword is used for implicit typing, in which the compiler chooses the type of the variable based on the value that is assigned to it. Explicit type declarations specify the variable's type explicitly. While var is concise, it's important to maintain code clarity, especially when dealing with complex types.

Top C# Coding Interview Questions and Answers

To prepare you for your technical interview, here are some basic and advanced C# coding interview questions and answers to get you started:

Q15. Name the different types of classes in C#.

The different classes in C# are:

1. Partial class - It lets members be divided or shared with multiple .cs files and is denoted by the keyword Partial.
2. Sealed class - This class cannot be inherited, and to access members of a sealed class, you need to create the object of the class. It’s denoted by the keyword Sealed.
3. Abstract class: It’s a class where the object can’t be instantiated and can only be inherited. Its keyword is abstract.
4. Static class - This class doesn’t allow inheritance, and the members are also static. It’s denoted by the keyword static.
   

Q16. Why is the virtual keyword used in code?

The virtual keyword is used for determining a class to specify that the methods and properties of that class can be overridden in derived classes. It supports polymorphism, allowing the derived classes to implement a particular implementation of the virtual members such that they still conform to the relevant contract set in the base class. It promotes flexibility and extensibility in object-oriented programming.

Q17. Why should you use finally block in C#?

The finally block will be carried out irrespective of exception. So when an exception occurs while executing the code in the try block, the control is given back to catch block, and then finally block is executed

It is also used to clean up resources, allowing the program to cleanly release those resources even if the actual execution ends in an error, preventing resource leaks.

Q18. List the advantages of C# as a programming language.

Some major advantages of using C# are:

• C# can be integrated with other technologies, languages, frameworks (such as .NET), or applications.
• It has a secure recovery system that ensures there aren’t any memory leaks.
• The library consists of an array of impressive tools that make implementation convenient.
  

Q19. Differentiate between method overriding and method overloading?

The difference between method overriding and overloading is as follows:

• Method overriding is defined as a redefinition of a method in a derived class, which already existed in the base class by the override keyword. This allows a subclass to provide its own implementation of a method.
• On the other hand, method overloading is defined as multiple methods with the same name but with different signatures or parameters within a single class, allowing flexibility in method invocation based on different parameter sets.

Q20. What’s the difference between dispose and finalize methods in C#?

Dispose method of C# is part of the IDisposable interface, which assists developers to explicitly release unmanaged resources such as file handles and database connections. Developers call it manually. 

Finalize method is also named destructor, which is automatically called by the garbage collector for cleaning up unmanaged resources whenever an object is no more in scope. Since Dispose is being called when a developer wants, there is no control in the hand of developers about what time Finalize will be executed, therefore Dispose will be preferable for timely resource management.

Q21. Give examples of some exceptions in C#.

Some exceptions in C# are:

• ArgumentNullException - It occurs when a null reference is passed to a method that doesn’t consider it as a valid argument.
• NullReferenceException - It shows an error when the user tries to gain access to a member on a type whose value is null.
• DivideByZeroException - It takes place when the user tries to divide an integral or decimal value by zero.
  

Q22. What is object pool in C#?

The object pool is responsible for tracking the objects used in the code when a request is made for a new object to reduce the object creation overhead. Objects are kept in a pool when they cannot be utilized and may be reused when a fresh request comes rather than making a new one each time. 

This eliminates the overhead of creating instances all the time and improves the performance of the system, mainly for resource-intensive applications.

Q23. How does the Sentinel Search work?

The purpose of linear search is to compare the search item with elements present in the list one at a time with the help of a loop and stop the moment the first copy of the search element in the list is obtained. If you consider the worst case in which the search element doesn’t exist in the list of size N, then the Simple Linear Search will consider a total of 2N+1 comparisons.

Coming to Sentinel Linear Search, the idea behind it is to cut down the number of comparisons needed to find an element in a list. In this, the last element of the list is replaced with the search element itself, and a while loop is run to determine if a copy of the search element in the list exists. The loop is quit as soon as the search element is found. It reduces one comparison in each repetition.

Q24. How to check if the two Strings (words) are Anagrams?

If two words contain the same number of characters and have the same number of characters, they’re anagrams. There are two solutions you can mention:

1. You can sort the characters using the lexicographic order and find out whether all the characters in one string are equal to the other string and are in the same order. If you sort either array, the solution will be - 0(n log n).
   

2. You can also go for the Hashmap approach in which key - letter and value - frequency of letter,

• For the first string, populate the hashmap 0(n)
• For the second string, decrement the count and then remove the element from hashmap 0(n)
• Only if the hashmap is empty are the strings an anagram; otherwise, they aren’t
  

Q25. How do you differentiate between Struct and a Class in C#?

Although class and struct both are user-defined data types, they do have some major differences:

Class

• It is a reference type in C# and inherits from the system.object type
• Usually used for large amounts of data
• Can be inherited to other class
• Can be the abstract type
  

Struct

• It is a value type in C# and inherits from the system.object Type
• Used for smaller amounts of data
• Can’t be inherited to other type
• Can’t be abstract
  

Q26. How can a class be prevented from overriding in C#?

In C#, we use the sealed keyword for a class so that no other can inherit from it. The class cannot be further extended. That is, no class can be derived from it. The reason is that sometimes a class provides a complete implementation that shall not be altered or extended further. Besides, individual methods can also be sealed inside the inheritable class to prevent them from being overridden in other derived classes.

Q27. Is there a distinction between throw and throw ex?

The difference between throw and throw ex is as follows:

• In throw ex, that thrown expectation becomes the ‘original’ one. All previous stack trace won’t be there.
• In throw, the exception just goes down the line, and you’ll get the full stack trace.

Q28. Explain the difference between Equality Operator (==) and Equals() Method in C#?

== Operator (usually means the same as ReferenceEquals, it can be overridden) is used to compare the reference identity. On the other hand, the Equals() (virtual Equals () )method compares whether two objects are equivalent.  

Q29. What’s the use of Null Coalescing Operator (??) in C#?

Known as the null-coalescing operator, the ?? operator defines a default value for nullable value types or reference types. It is responsible for returning the left-hand operand if the operand is not null. Else, it returns the right operand.

Extra C# Coding Interview Questions For Practice

When you’re preparing for the technical interview, ensure that you prepare the following C# coding interview questions as well. These will come in handy to experienced professionals as well as freshers.

1. Which C# structure would you use to get the fastest large objects manipulation?
2. Which C# features do you like the most and why?
3. How, according to you, can a great # code be written?
4. Explain the difference between interface and abstract class?
5. Will you be able to write the FizzBuzz program in C# now?
6. What is LINQ in C#? Have you ever used it?
7. Define Dynamic Dispatch.
8. What makes your code really object-oriented?
9. How to avoid the NULL trap?
10. List the fundamental principles of Object Oriented Programming?
11. Name three ways to pass parameters to a method in C#.
12. Give some features of generics in C#.
13. What are delegates and their types in C#?
14. Compare ‘string’ and ‘StringBuilder’ in C#.
15. In C#, what’s the differentiating factor between an abstract class and an interface?

Ace Your Next Technical Interview With Interview Kickstart

You can get better at C# just by practicing and refreshing the fundamental concepts. With these C# coding interview questions and answers, you will be able to crack any technical interview. With Interview Kickstart, you can fast track your interview prep and clear any tech interview.

At IK, you get the unique opportunity to learn from expert instructors who are hiring managers and tech leads at Google, Facebook, Apple, and other top Silicon Valley tech companies. Our reviews will tell you how we’ve shaped the careers of thousands of professionals aspiring to take their careers to new heights.

FAQs: C# Coding Interview Questions

Q1. What interview are questions asked in C#?

Some C# coding interview questions are: Give examples of the different types of comments in C#. Differentiate between public, static, and void. What are Jagged Arrays?

Q2. Which topics are asked in C# coding interview questions?

Some important topics when preparing for C# interview questions are: CLR, CLS, CTS, Classes & Objects, and OOPs.

Q3. How do you differentiate between C# and C?

The difference between C# and C is given as follows:

Q4. What is the extension method in C# interview questions?

The extension method is a static method of a static class and can be used with the help of the instance method syntax. Extension methods are useful in adding new behaviors to an existing type without altering anything.

Q5. How do you prepare for C# coding interview questions?

Keep your C# basics on point and practice mock interviews. You can even take part in coding competitions to improve your speed and accuracy.

Related Reads:

• Most Important OOPs Interview Questions
• Object-Oriented Programming (OOP) MCQs for Software Developers
• Java OOPs Interview Questions to Crack Coding Interviews