Mahedee Hasan

Mahedee Hasan

I am a Microsoft MVP (11th times), programmer, software developer, software architect, consultant, author, researcher, technical blogger, technical speaker, trainer and learner. I have more than 17 years experience in the field of software design and development.

Master C# Interviews: 100 Essential Questions Every Developer Should Know

8 minute read

Preparing for a C# developer interview? Whether you’re a fresh graduate or a seasoned professional looking to advance your career, having a solid understanding of C# concepts is crucial. This comprehensive guide presents 100 carefully curated C# interview questions that cover everything from basic syntax to advanced programming concepts.

Table of Contents

Beginner Level Questions (1-50)

C# Fundamentals and Basic Concepts

1. What is value type and reference type?

2. What is C# and what are its main features?

3. What is class? Give a real life example.

4. What is Object? Give a real life example.

5. Why C# is called strongly typed language? What are the benefits of strongly typed language?

6. What is the difference between a class and a struct in C#?

7. When do we use struct instead of class in c#?

8. Which datatypes are implemented as struct and which are class in c#?

9. What is predefined data type and user defined data type? Discuss with example.

10. What is the difference between a static class and a non-static class in C#?

Variables, Constants, and Data Types

11. What is verbatim string? How it works?

12. What is the difference between String and StringBuilder in C#? Explain with example and expected output.

13. Why and how constant is used in C#?

14. What is the difference between read only and constant variable?

15. Why read only variable is used?

16. What is enumeration type? How it works?

17. What do you know implicit and explicit conversion? Give an example.

18. What is boxing and unboxing?

19. Why boxing and unboxing is necessary in C#? Explain with example.

20. Explain a scenario with example where boxing and unboxing required.

Control Structures and Operators

21. How switch statement works? What is the function of default in switch case?

22. How break and continue keyword works? Give an example.

23. What is the difference in for loop, while loop and do while loop?

24. Is there any difference between “++i” and “i++”? How it works?

25. What is the difference between the “ref” and “out” keywords in C#?

Object-Oriented Programming Basics

26. What is constructor? What is constructor overloading?

27. Why constructor is used?

28. What is inheritance? Why is it necessary?

29. How do you implement multiple inheritance in C#?

30. What is method overloading and method overriding in C#?

31. Give an example of method overloading and method overriding?

32. foo and foo(int i =0) is it method over loading in c#? How to call this two method?

33. What is abstract class?

34. What is sealed class? Why sealed class is used?

35. Can you explain the difference between abstract classes and interfaces in C#?

Basic Programming Concepts

36. What do you know about namespace and nested namespace? Why namespace is used?

37. How parameter is passed by reference? Give an example.

38. In C# how do return multiple value? Explain with example.

39. What is the use of dispose method?

40. Why partial class?

Collections and Basic LINQ

41. What is the difference between a HashSet and a List in C#? Explain with example.

42. What is the difference between IEnumerable and List in C#? Explain with example.

43. What is AddRange method? How it works? Explain with example.

44. Why hashtable is faster? Explain with C# example and write expected output.

Basic Exception Handling

45. What is exception handling in C#?

46. What are the different types of exceptions in C#?

47. How do you handle exceptions using try-catch blocks?

48. What is the finally block and when is it used?

49. What is the difference between throw and throw ex?

50. How do you create custom exceptions in C#?

Advanced/Senior Level Questions (51-100)

Advanced Object-Oriented Programming

51. What are extension methods in C#? Give an example of extension method in c#?

52. What is a delegate in C#? Explain different types of delegates with example.

53. What is the difference between an event and a delegate in C#? Explain with example.

54. What is callback method in C#? When it is used? Explain with some examples.

55. What is a lambda expression in C#? Explain with some example.

56. What is expression tree in c#? Explain with an example.

Generics and Advanced Types

57. What are generic constraints in c#? Explain with example.

58. How many types of generic constraints in C#?

59. Can you apply where T : new constraint in C# using an example.

60. What are limitations of generics in c#?

61. What is dynamic object in C#. Explain with an example.

Collections and LINQ

62. What is the difference between IEnumerable and IQueryable in C#? Explain with example.

63. Why ToList method is used in the following code?

64. Write a LINQ Query to find the uncommon element from the two lists.

65. What are the different types of LINQ operators?

Asynchronous Programming

66. What is asynchronous programming? What is the benefit? Explain with C# example.

67. Give me an example of Asynchronous Programming.

68. What is the difference between “async” and “await” in C#? Explain with example.

69. What is the disadvantages of asynchronous programming?

70. Explain Callback Hell and Race Conditions using C# example.

Multithreading and Concurrency

71. What is multi-threaded programming?

72. Explain multi-threaded programming with an example of C#?

73. What is the benefit of multi-threaded programming?

74. What is dead lock? Explain with C# example and its output.

75. How avoid deadlock? Explain with C# example and output.

Memory Management and Performance

76. What is the difference between a shallow copy and a deep copy in C#? Explain with example.

77. What is garbage collection in C#?

78. How does memory management work in C#?

79. What are generations in garbage collection?

80. What is the difference between Dispose and Finalize methods?

Reflection and Advanced Features

81. What is reflection? Why do you use reflection? Explain with an example in C#.

82. Write a sample code using c# to access the assembly of a running application.

83. What will be the correct code to make sure that method doesn’t have exceptions or invalid conversions?

84. What is the uses of following method in C#? Explain with example.

Entity Framework and Database

85. How to Bulk insert, update and delete in Entity framework core?

86. What is Lazy, Eager and Explicit Loading in Entity Framework? Explain with example.

87. What is Code First approach in Entity Framework?

88. What is the difference between DbContext and ObjectContext?

Testing and Best Practices

89. What is xUnit? How xUnit works with C#? Explain with example.

90. What is dependency injection in C#?

91. What are the SOLID principles?

92. How do you implement the Repository pattern in C#?

Advanced Language Features

93. What is yield keyword in C#?

94. What are nullable reference types in C#?

95. What is pattern matching in C#?

96. What are records in C#?

97. What is the difference between var and dynamic keywords?

98. What are tuples in C#?

99. Write C# code for the following statement.

100. Explain the new features introduced in the latest version of C#.

Interview Preparation Tips

For Beginner Positions:

  • Focus on fundamental OOP concepts and C# syntax
  • Practice writing simple programs and understanding basic data structures
  • Understand exception handling and basic LINQ operations
  • Know the difference between value and reference types
  • Be comfortable with loops, conditionals, and method declarations

For Advanced/Senior Positions:

  • Deep understanding of asynchronous programming and multithreading
  • Advanced LINQ operations and Entity Framework
  • Design patterns and architectural principles
  • Performance optimization and memory management
  • Testing methodologies and best practices

General Preparation Strategy:

  • Practice coding problems on platforms like LeetCode or HackerRank
  • Build small projects to demonstrate practical knowledge
  • Review the latest C# language features and .NET updates
  • Understand when and why to use different design patterns
  • Be prepared to discuss real-world scenarios and problem-solving approaches

Recently Updated Questions

Reviewed and Updated 01: Recently Updated - Last point reviewed.

Here are some of the most commonly asked questions in recent interviews:

Modern C# Features:

  • How do you use nullable reference types in your projects?
  • What are the benefits of using records over traditional classes?
  • Explain the new pattern matching features in C# 9.0 and above.

Cloud and Microservices:

  • How do you implement configuration management in .NET Core applications?
  • What is the difference between .NET Framework and .NET Core/.NET 5+?
  • How do you implement health checks in ASP.NET Core applications?

Performance and Optimization:

  • How do you optimize LINQ queries for better performance?
  • What are the best practices for memory management in high-performance applications?
  • How do you implement caching strategies in C# applications?

Testing and Quality:

  • How do you implement unit testing with mocking frameworks?
  • What is the difference between integration testing and unit testing?
  • How do you implement test-driven development (TDD) in C#?

Interview Experience Sharing

We want to hear from you!

Have you recently been through a C# developer interview? We’d love to learn about your experience! Please share in the comments below:

  • What questions were you asked that aren’t covered in this list?
  • Which topics were emphasized the most in your interview?
  • Any unexpected questions or coding challenges you encountered?
  • Tips and advice for other developers preparing for interviews

Your insights help keep this guide current and valuable for the developer community. Whether you’re a recent graduate who just landed your first job or a senior developer who moved to a new company, your experience matters!

Recent Interview Trends:

  • More focus on cloud-native development and containerization
  • Emphasis on microservices architecture and API design
  • Questions about DevOps practices and CI/CD pipelines
  • Increased attention to security best practices
  • Focus on clean code principles and design patterns

Conclusion

This comprehensive list of 100 C# interview questions covers the full spectrum of knowledge expected from C# developers at different experience levels. Remember that successful interviews are not just about memorizing answers, but about understanding concepts deeply and being able to apply them to solve real-world problems.

Key Success Factors:

  • Understand the “why” behind each concept, not just the “what”
  • Practice coding regularly to maintain your skills
  • Stay updated with the latest C# and .NET developments
  • Build projects that demonstrate your knowledge practically
  • Prepare examples from your actual work experience

Whether you’re preparing for your first C# developer role or advancing to a senior position, these questions will help you assess your knowledge and identify areas for improvement.

Good luck with your interviews! Remember to stay calm, think through your answers, and don’t hesitate to ask for clarification if needed.

Have questions about any of these topics or want to contribute additional interview questions? Please leave a comment below and help fellow developers in their interview preparation journey!

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