Top 30 Most Common C Sharp Interview Questions You Should Prepare For
Written by
James Miller, Career Coach
Navigating the landscape of technical interviews can feel daunting, especially when aiming for roles involving C#. Developers often face a barrage of questions testing their understanding of language fundamentals, object-oriented principles, data structures, and specific frameworks like Entity Framework or ASP.NET Core. Acing these interviews requires not just knowing the answers, but understanding the why behind the concepts and being able to articulate them clearly and concisely. This article provides a comprehensive guide to 30 of the most frequently asked c sharp interview questions, offering insights into why they are asked, how to approach your answer, and providing example responses to help you prepare effectively. Whether you're a recent graduate or an experienced professional looking to level up your career, mastering these c sharp interview questions is a crucial step toward demonstrating your proficiency and landing your desired position. Preparing for c sharp interview questions involves reviewing core language features, common pitfalls, and best practices used in real-world development scenarios. This structured approach ensures you cover essential topics.
What Are C Sharp Interview Questions?
C sharp interview questions are a set of technical inquiries designed to assess a candidate's knowledge and proficiency in the C# programming language and its associated ecosystem, primarily the .NET framework. These questions cover a wide range of topics, from foundational concepts like data types, variables, and control structures, to more advanced areas such as object-oriented programming (OOP) principles, exception handling, collections, delegates, events, and multithreading. Furthermore, c sharp interview questions often delve into framework-specific knowledge relevant to the role, such as ASP.NET Core for web development, WPF for desktop applications, or Entity Framework for data access. The complexity and depth of these c sharp interview questions typically vary depending on the seniority level of the position, ranging from basic syntax and feature recall for junior roles to complex design patterns, performance optimization, and architectural considerations for senior or lead developer positions. Preparing for these c sharp interview questions is key.
Why Do Interviewers Ask C Sharp Interview Questions?
Interviewers ask c sharp interview questions for several key reasons. Firstly, they serve as a fundamental technical screening tool to verify that a candidate possesses the requisite knowledge and skills for the job. Simply listing C# on a resume isn't enough; candidates must demonstrate a solid understanding of the language's core concepts and capabilities. Secondly, these c sharp interview questions help evaluate a candidate's problem-solving abilities and their approach to writing clean, efficient, and maintainable code. Questions often involve explaining concepts or contrasting different approaches (like String vs StringBuilder), revealing how a candidate thinks critically about code design and performance. Thirdly, discussing specific c sharp interview questions allows interviewers to gauge a candidate's practical experience and familiarity with common development scenarios, such as handling exceptions, managing collections, or interacting with databases using technologies like Entity Framework. Finally, the way a candidate answers c sharp interview questions provides insight into their communication skills, their ability to articulate complex technical ideas clearly, and their overall enthusiasm for software development. Mastering c sharp interview questions shows dedication.
Preview List
What is C#?
What are the main features of C#?
What is the difference between a class and an object?
What is inheritance in C#? Does C# support multiple inheritance?
What is the difference between
StringandStringBuilder?What are partial classes?
Explain the difference between virtual and abstract methods.
What are namespaces in C#?
What is the difference between
throwandthrow exin exception handling?What is the role of the
finallyblock?How do you create a custom exception?
What is the difference between List, Array, and Dictionary?
What is the difference between EF Core and EF6?
What is lazy loading in Entity Framework?
How do you implement migrations in EF Core?
What is an abstract class? How is it different from an interface?
Can an abstract class have constructors?
What is multithreading in C#?
What are delegates?
What is the difference between an interface and a class?
What are events in C#?
How do you secure a C# Web API?
Difference between GET and POST in APIs?
How do you return custom responses from a controller?
What is the use of
HashSet?What is the time complexity of accessing elements in a List?
What is exception handling best practice?
How does C# handle memory management?
Write a program to find the second-largest number in an array.
What is boxing and unboxing?
1. What is C#?
Why you might get asked this:
Tests your fundamental understanding of the language's identity, purpose, and platform. It's a basic entry-level question for c sharp interview questions.
How to answer:
Define C# concisely, mentioning its origin, type, and the framework it runs on. Highlight its main characteristics briefly.
Example answer:
C# is a modern, object-oriented programming language developed by Microsoft. It runs on the .NET framework and is designed for building various applications, from web services to desktop apps. It's known for being type-safe and component-oriented.
2. What are the main features of C#?
Why you might get asked this:
Assesses your awareness of the key capabilities and design principles that make C# a popular and powerful language. Relevant for c sharp interview questions.
How to answer:
List and briefly explain several prominent features like OOP, strong typing, garbage collection, etc.
Example answer:
Key features include object-orientation, strong typing, component-orientation, automatic garbage collection, and support for robust exception handling. It also supports properties, events, and delegates, which are core to its design.
3. What is the difference between a class and an object?
Why you might get asked this:
Checks your grasp of fundamental object-oriented programming concepts, essential for any C# developer role.
How to answer:
Explain the relationship using the blueprint/instance analogy. Define each term distinctly.
Example answer:
A class is a blueprint or template that defines the structure and behavior (data members and methods) for objects. An object is an instance of a class, representing a concrete entity created based on the class definition, with actual data values.
4. What is inheritance in C#? Does C# support multiple inheritance?
Why you might get asked this:
Evaluates your understanding of a core OOP principle and its specific implementation nuances in C#. A common topic in c sharp interview questions.
How to answer:
Define inheritance and explain how it works in C#. Clarify C#'s stance on multiple inheritance for classes vs. interfaces.
Example answer:
Inheritance allows a new class (derived class) to inherit properties and behaviors from an existing class (base class). C# supports single inheritance for classes, meaning a class can only inherit from one base class. However, it supports multiple interface inheritance.
5. What is the difference between String and StringBuilder?
Why you might get asked this:
Tests your knowledge of string manipulation performance and efficiency, crucial for avoiding common performance issues. A practical question for c sharp interview questions.
How to answer:
Explain the mutability difference and its implication on performance, especially during frequent modifications.
Example answer:
String objects are immutable; operations that appear to modify a string actually create a new string object. StringBuilder is mutable; it allows modifications to a string without creating a new object each time, making it efficient for repeated appending or manipulation.
6. What are partial classes?
Why you might get asked this:
Assesses your familiarity with a language feature used to split class definitions, often seen in generated code or large projects.
How to answer:
Explain the purpose of partial classes – splitting the definition across multiple files. Mention its common uses.
Example answer:
Partial classes allow you to split the definition of a class, struct, or interface across multiple source files. All parts are combined by the compiler into a single definition. This is useful for large classes or separating auto-generated code from manual code.
7. Explain the difference between virtual and abstract methods.
Why you might get asked this:
Checks your understanding of polymorphic behavior and class design using abstract and concrete implementations. Key for OOP c sharp interview questions.
How to answer:
Define each method type and clearly state their key differences regarding implementation and requirement for overriding.
Example answer:
A virtual method has a default implementation in the base class but can be overridden by derived classes. An abstract method has no implementation in the abstract base class; it must be implemented (overridden) by any concrete derived class.
8. What are namespaces in C#?
Why you might get asked this:
Evaluates your understanding of code organization and how C# prevents naming conflicts in larger applications or when using external libraries.
How to answer:
Define namespaces as a way to organize code and prevent name clashes. Explain their purpose in grouping related types.
Example answer:
Namespaces are used to organize code and provide a way to manage the scope of names defined in a class or assembly. They group related types (classes, structs, interfaces, enums, delegates) and help avoid naming conflicts when combining code from different sources.
9. What is the difference between throw and throw ex in exception handling?
Why you might get asked this:
Tests your knowledge of best practices in exception handling and understanding how re-throwing affects the stack trace. Crucial for robust c sharp interview questions.
How to answer:
Explain that throw preserves the original stack trace, while throw ex overwrites it, obscuring the original error location.
Example answer:
throw; (without the exception object) rethrows the caught exception while preserving the original stack trace, showing where the error originally occurred. throw ex; resets the stack trace to the point where the exception is rethrown, losing the original context.
10. What is the role of the finally block?
Why you might get asked this:
Assesses your understanding of resource management and guaranteeing code execution regardless of exceptions, a vital part of exception handling.
How to answer:
Explain that the finally block is executed unconditionally after the try or catch block, and mention its common use for cleanup.
Example answer:
The finally block is used in exception handling to contain code that must be executed regardless of whether an exception occurs or not in the try block, or if it's caught in the catch block. It's typically used for releasing resources like file handles or database connections.
11. How do you create a custom exception?
Why you might get asked this:
Tests your ability to extend the exception handling mechanism for specific application errors, showing a deeper understanding of the topic.
How to answer:
Explain the process of inheriting from System.Exception and optionally implementing standard constructors.
Example answer:
To create a custom exception, you define a new class that inherits directly or indirectly from System.Exception. It's good practice to include the standard constructors (parameterless, message, message and inner exception, serialization) to align with .NET conventions.
12. What is the difference between List, Array, and Dictionary?
Why you might get asked this:
Evaluates your knowledge of fundamental collection types and when to use each based on requirements like size flexibility, access patterns, and key-value storage.
How to answer:
Describe each collection type's characteristics (fixed/dynamic size, indexing, key-value) and suggest appropriate use cases.
Example answer:
An Array is a fixed-size, strongly-typed collection accessed by index. List is a dynamic-size, generic collection offering flexible element insertion/removal and index access. Dictionary stores key-value pairs, optimized for fast retrieval by key.
13. What is the difference between EF Core and EF6?
Why you might get asked this:
Checks your familiarity with modern data access technologies in the .NET ecosystem, especially if the role involves newer projects. Relevant for data-focused c sharp interview questions.
How to answer:
Highlight key differences like platform compatibility, performance, and architectural changes.
Example answer:
EF Core is a modern, lightweight, extensible, and cross-platform version of Entity Framework. EF6 is the mature, feature-rich Object-Relational Mapper for .NET, primarily Windows-based. EF Core generally offers performance improvements and is designed for newer .NET platforms.
14. What is lazy loading in Entity Framework?
Why you might get asked this:
Assesses your understanding of how EF loads related data and the performance implications of different loading strategies.
How to answer:
Define lazy loading as delaying the loading of related data until it's accessed. Mention its potential pros and cons (reduced initial query vs. N+1 problem).
Example answer:
Lazy loading in Entity Framework defers loading related entities until they are specifically referenced. Instead of loading all related data with the initial query, it fetches the data on demand. This can reduce the size of initial query results but might lead to performance issues if many related objects are accessed in a loop (N+1 problem).
15. How do you implement migrations in EF Core?
Why you might get asked this:
Tests your practical knowledge of managing database schema changes alongside code changes using a common EF Core feature.
How to answer:
Describe the basic command-line steps involved: creating a migration and applying it to the database.
Example answer:
In EF Core, migrations are implemented using command-line tools. You use Add-Migration [MigrationName] to scaffold a migration based on changes in your DbContext. Then, you apply the changes to the database using Update-Database or by generating SQL scripts.
16. What is an abstract class? How is it different from an interface?
Why you might get asked this:
Evaluates your understanding of polymorphism and design choices between providing partial implementation (abstract class) and defining a contract (interface).
How to answer:
Define both abstract classes and interfaces. Focus on the key differences: implementation capability, constructors, and multiple inheritance rules.
Example answer:
An abstract class can have both abstract members (no implementation) and concrete members (with implementation). It can also have constructors and state. An interface defines a contract of public members without any implementation or state. A class can inherit from one abstract class but multiple interfaces.
17. Can an abstract class have constructors?
Why you might get asked this:
A specific detail testing whether you understand the initialization process when working with abstract classes and inheritance.
How to answer:
Confirm that they can and explain their purpose in initializing the state inherited by derived classes.
Example answer:
Yes, an abstract class can have constructors. These constructors are used to initialize the members of the abstract class when a concrete derived class is instantiated, similar to how constructors work in non-abstract base classes.
18. What is multithreading in C#?
Why you might get asked this:
Checks your understanding of concurrent programming, essential for building responsive and efficient applications, especially in modern systems. A key topic for intermediate/senior c sharp interview questions.
How to answer:
Define multithreading as executing multiple parts of a program concurrently. Mention its benefits like improved responsiveness and utilization of multi-core processors.
Example answer:
Multithreading is the ability of a program to run multiple threads concurrently. Each thread can execute code independently. This allows applications to perform time-consuming tasks in the background while keeping the main thread responsive, improving performance on multi-core systems.
19. What are delegates?
Why you might get asked this:
Assesses your knowledge of type-safe function pointers and their role in event handling, callbacks, and LINQ.
How to answer:
Define delegates as type-safe references to methods (function pointers). Explain their primary use cases.
Example answer:
A delegate is a type that represents references to methods with a particular parameter list and return type. They are type-safe function pointers. Delegates are fundamental to implementing events, callback mechanisms, and are widely used in LINQ and other areas of the .NET framework.
20. What is the difference between an interface and a class?
Why you might get asked this:
Similar to the abstract class comparison, this checks your understanding of contracts versus implementations in OOP design.
How to answer:
Clearly define each and highlight the core difference: interface defines what a class must do (contract), class defines how it does it (implementation and state).
Example answer:
An interface is a contract that specifies a set of members (methods, properties, events, indexers) that implementing classes must provide. It contains no implementation details. A class is a blueprint for creating objects, containing data members and method implementations. A class implements interfaces and can inherit from a single base class.
21. What are events in C#?
Why you might get asked this:
Tests your understanding of the observer pattern and how C# implements notifications and loosely coupled communication between objects. Often paired with delegates in c sharp interview questions.
How to answer:
Define events as a mechanism for broadcasting notifications. Explain their dependency on delegates and their role in object communication.
Example answer:
Events are a member of a class used to provide notifications to other objects when something of interest happens. They are built upon the delegate infrastructure. Objects subscribe to events using delegates, allowing for a loosely coupled communication pattern (publisher-subscriber).
22. How do you secure a C# Web API?
Why you might get asked this:
Crucial for roles involving web development; assesses your awareness of security best practices for protecting APIs from common threats.
How to answer:
Mention key security concepts like authentication, authorization, using HTTPS, and validating inputs.
Example answer:
Securing a C# Web API involves several layers: implementing authentication (e.g., JWT, OAuth) to verify caller identity, authorization to control access to resources, using HTTPS to encrypt data in transit, and rigorous input validation to prevent injection attacks.
23. Difference between GET and POST in APIs?
Why you might get asked this:
Tests your knowledge of fundamental HTTP methods used in web development, essential for understanding API design.
How to answer:
Explain their primary purpose (retrieval vs. submission) and how parameters are typically handled.
Example answer:
GET requests are used to retrieve data from the server and should be idempotent (multiple identical requests have the same effect). Parameters are typically sent in the URL query string. POST requests are used to send data to the server to create or update a resource. Data is sent in the request body, and requests are not necessarily idempotent.
24. How do you return custom responses from a controller?
Why you might get asked this:
Evaluates your practical skills in building Web APIs, specifically how to control the HTTP response status code and body.
How to answer:
Mention using IActionResult or ActionResult and returning built-in helper methods like Ok(), NotFound(), BadRequest(), or custom objects wrapped in Ok().
Example answer:
In ASP.NET Core controllers, you typically return types derived from IActionResult or use ActionResult. You can return built-in helper results like Ok(), NotFound(), BadRequest(), StatusCode(), or return data objects which the framework formats (e.g., as JSON) often wrapped in an Ok() call.
25. What is the use of HashSet?
Why you might get asked this:
Checks your knowledge of specialized collection types and when to use them for specific performance benefits.
How to answer:
Describe its purpose: storing unique elements and its performance characteristics for key operations.
Example answer:
HashSet is used to store a collection of unique elements. Its main advantage is very fast performance (O(1) on average) for add, remove, and contains operations, making it ideal for checking for the existence of items quickly.
26. What is the time complexity of accessing elements in a List?
Why you might get asked this:
Tests your understanding of fundamental data structure performance characteristics, important for writing efficient code.
How to answer:
State the complexity for accessing by index and the complexity for searching by value.
Example answer:
Accessing an element in a List by its index is a constant time operation, O(1). Searching for a specific element by value typically requires iterating through the list, resulting in a linear time complexity, O(n).
27. What is exception handling best practice?
Why you might get asked this:
Assesses your understanding of writing robust and maintainable code that gracefully handles errors without hiding information or causing resource leaks.
How to answer:
List several key practices: catching specific exceptions, using finally for cleanup, avoiding empty catch blocks, and logging exceptions appropriately.
Example answer:
Best practices include catching specific exception types rather than generic Exception, using finally blocks for resource cleanup, avoiding empty catch blocks that swallow errors, logging exceptions for debugging, and rethrowing exceptions when necessary using throw; to preserve the stack trace.
28. How does C# handle memory management?
Why you might get asked this:
Evaluates your understanding of the runtime environment and how objects are allocated and deallocated, particularly the role of the garbage collector.
How to answer:
Explain the concept of automatic garbage collection and how it manages memory for objects on the managed heap.
Example answer:
C# uses automatic memory management through a garbage collector (GC). Objects are allocated on the managed heap. When objects are no longer referenced, the GC automatically reclaims the memory they occupied. This frees developers from manual memory deallocation tasks.
29. Write a program to find the second-largest number in an array.
Why you might get asked this:
A common coding challenge question testing your algorithm skills, array manipulation, and potentially sorting or iteration logic.
How to answer:
Provide a concise algorithm or pseudo-code. A common approach is to iterate, keeping track of the largest and second-largest numbers seen so far. Avoid simple sorting if asked for efficiency.
Example answer:
Initialize two variables, largest and secondLargest, to negative infinity or the first two distinct elements. Iterate through the array: if an element is greater than largest, update secondLargest to largest and largest to the element. Else if it's greater than secondLargest and not equal to largest, update secondLargest.
30. What is boxing and unboxing?
Why you might get asked this:
Tests your understanding of the interaction between value types and reference types, and the performance implications of type conversions.
How to answer:
Define both boxing (value to object) and unboxing (object to value) and mention the potential performance cost.
Example answer:
Boxing is the process of converting a value type (like int, struct) to a reference type (object or any interface type implemented by the value type). Unboxing is the explicit conversion of an object type back to a value type. These conversions involve overhead and can impact performance if done frequently.
Other Tips to Prepare for a C Sharp Interview Questions
Successfully navigating c sharp interview questions involves more than just memorizing answers. It requires practice and confidence. One effective strategy is to practice explaining concepts out loud or to a peer. As the saying goes, "If you can't explain it simply, you don't understand it well enough." Reviewing fundamental data structures and algorithms in C# is also crucial, as coding challenges are a staple of technical interviews. Practice solving problems on platforms like LeetCode or HackerRank using C#. Familiarize yourself with the .NET framework's standard libraries and common patterns. Stay updated on recent C# versions and .NET developments. For targeted practice answering c sharp interview questions under pressure, consider utilizing tools like Verve AI Interview Copilot. Verve AI Interview Copilot offers mock interviews with AI tailored to specific technologies like C#, providing instant feedback on your responses, clarity, and technical accuracy. This can significantly boost your confidence. Explore personalized AI interview practice at https://vervecopilot.com. Remember, preparation reduces nervousness and allows your knowledge to shine through. "The best way to predict the future is to create it," and diligent preparation for c sharp interview questions is creating your future career opportunity. Using resources like Verve AI Interview Copilot helps refine your articulation of technical answers.
Frequently Asked Questions
Q1: How long should my answers to c sharp interview questions be?
A1: Aim for concise, clear answers that directly address the question, typically 1-3 sentences for definitions and slightly longer for explanations.
Q2: Should I write code during the interview?
A2: Yes, be prepared for coding challenges. Practice writing clean, functional code on a whiteboard or shared editor.
Q3: How can I practice answering c sharp interview questions?
A3: Review concepts, explain them aloud, use flashcards, practice coding problems, and consider using AI tools like Verve AI Interview Copilot for mock interviews.
Q4: What if I don't know the answer to a question?
A4: Be honest. Say you don't know but offer to explain a related concept or how you would approach finding the answer.
Q5: Are there different types of c sharp interview questions?
A5: Yes, they range from theoretical knowledge, problem-solving (coding), scenario-based, to behavioral questions. This list focuses on technical C# knowledge.
Q6: Should I ask questions at the end of the interview?
A6: Absolutely. Asking thoughtful questions shows your interest in the role and the company.
