C# Interview Questions and Answers for 5 years experience

1. What is the difference between `string` and `StringBuilder` in C#?

   • Answer: `string` is immutable; each operation creates a new string object. `StringBuilder` is mutable, modifying the existing object in place, making it significantly more efficient for string manipulation involving many concatenations or modifications.

2. Explain the concept of garbage collection in C#.

   • Answer: Garbage collection is an automatic memory management process. The .NET runtime identifies objects that are no longer referenced by the application and reclaims the memory they occupy. This prevents memory leaks and simplifies development.

3. What are delegates and events in C#? Give an example.

   • Answer: Delegates are type-safe function pointers. Events use delegates to provide a mechanism for one object to notify other objects when something significant happens. Example: A button click event uses a delegate to point to the method that handles the click.

4. What is LINQ and how does it work?

   • Answer: LINQ (Language Integrated Query) allows you to query data from various sources (databases, XML, collections) using a consistent syntax. It translates queries into efficient code that interacts with the data source.

5. Explain the different types of access modifiers in C# (public, private, protected, internal, protected internal).

   • Answer: `public`: Accessible from anywhere. `private`: Accessible only within the class. `protected`: Accessible within the class and derived classes. `internal`: Accessible within the same assembly. `protected internal`: Accessible within the same assembly and derived classes.

6. What is the difference between a `List` and an array in C#?

   • Answer: `List` is a dynamic array that can resize itself as needed. Arrays have a fixed size determined at creation. `List` offers methods for adding, removing, and searching elements, while arrays require manual management.

7. What is polymorphism in C#? Give an example.

   • Answer: Polymorphism allows objects of different classes to be treated as objects of a common type. Example: A base class `Animal` with a `MakeSound()` method. Derived classes like `Dog` and `Cat` override `MakeSound()` to produce different sounds.

8. Explain inheritance in C#.

   • Answer: Inheritance is a mechanism where a class (derived class) inherits properties and methods from another class (base class). It promotes code reusability and establishes an "is-a" relationship.

9. What is the purpose of the `using` statement in C#?

   • Answer: The `using` statement ensures that IDisposable objects (like files, network connections) are properly disposed of, even if exceptions occur. It automatically calls the `Dispose()` method.

10. What is exception handling in C# and how do you implement it?

    • Answer: Exception handling is a mechanism to gracefully handle runtime errors. It uses `try`, `catch`, and `finally` blocks. `try` contains code that might throw an exception, `catch` handles specific exceptions, and `finally` executes regardless of whether an exception occurred.

11. Explain the difference between `ref` and `out` parameters in C#.

    • Answer: `ref` parameters require the variable to be initialized before passing it to the method. `out` parameters don't require initialization; the method is responsible for assigning a value.

12. What are interfaces in C#?

    • Answer: Interfaces define a contract that classes must adhere to. They specify methods, properties, and events that a class must implement. They support polymorphism and loose coupling.

13. What are generics in C#? What are their benefits?

    • Answer: Generics allow you to write type-safe code that can work with different data types without losing type information at compile time. Benefits include type safety, performance improvements, and code reusability.

14. Explain the concept of asynchronous programming in C# using `async` and `await`.

    • Answer: `async` and `await` keywords enable asynchronous programming, allowing long-running operations (like network requests) to execute without blocking the main thread, improving responsiveness.

15. What is a lambda expression in C#?

    • Answer: A lambda expression is an anonymous function that can be used to create delegates or expression tree types.

16. What is the difference between a value type and a reference type in C#?

    • Answer: Value types (like `int`, `float`, `struct`) store data directly on the stack. Reference types (like `class`, `string`) store a reference to the data on the heap.

17. Explain the concept of boxing and unboxing in C#.

    • Answer: Boxing is converting a value type to a reference type (like `object`). Unboxing is converting a reference type back to a value type.

18. What are properties in C#?

    • Answer: Properties provide a controlled way to access and modify the fields of a class. They encapsulate the data and can add validation or other logic.

19. What is dependency injection in C#?

    • Answer: Dependency injection is a design pattern where dependencies are provided to a class instead of being created within the class. This improves testability and loose coupling.

20. Explain different ways to implement dependency injection in C#.

    • Answer: Constructor injection, property injection, and method injection.

21. What are design patterns? Name a few commonly used design patterns.

    • Answer: Design patterns are reusable solutions to common software design problems. Examples: Singleton, Factory, Observer, MVC.

22. What is the purpose of the `static` keyword in C#?

    • Answer: The `static` keyword indicates that a member (method, field, class) belongs to the class itself, not to any specific instance of the class.

23. What is the difference between `const` and `readonly` in C#?

    • Answer: `const` values are compile-time constants. `readonly` values can be assigned at declaration or in a constructor.

24. Explain the concept of multithreading in C#.

    • Answer: Multithreading allows multiple parts of a program to execute concurrently, improving performance, especially on multi-core processors.

25. How do you handle thread synchronization in C#?

    • Answer: Using locks (mutexes), semaphores, or other synchronization primitives to prevent race conditions and ensure data consistency.

26. What is the difference between a thread and a process?

    • Answer: A process is an independent execution environment. A thread is a unit of execution within a process.

27. What is the role of the `Task` class in C#?

    • Answer: The `Task` class represents an asynchronous operation. It simplifies asynchronous programming and provides methods for managing tasks.

28. What is the purpose of the `CancellationToken` class?

    • Answer: `CancellationToken` allows cooperative cancellation of asynchronous operations. It provides a mechanism for a task to check if it should be stopped.

29. Explain different ways to serialize and deserialize objects in C#.

    • Answer: Using `BinaryFormatter`, `XmlSerializer`, `DataContractSerializer`, or Newtonsoft.Json (Json.NET).

30. What are attributes in C#? Give an example.

    • Answer: Attributes provide metadata about code elements. Example: `[Serializable]` attribute marks a class as serializable.

31. What is reflection in C#?

    • Answer: Reflection allows you to inspect and manipulate types, members, and assemblies at runtime.

32. What is the purpose of the `params` keyword in C#?

    • Answer: `params` allows a method to accept a variable number of arguments of a specific type.

33. What is a jagged array in C#?

    • Answer: A jagged array is an array of arrays, where each inner array can have a different size.

34. What is the difference between `virtual`, `abstract`, and `override` keywords?

    • Answer: `virtual` methods can be overridden in derived classes. `abstract` methods must be overridden. `override` is used to implement the overridden method.

35. What are extension methods in C#?

    • Answer: Extension methods allow you to add new methods to existing types without modifying their original source code.

36. Explain the concept of operator overloading in C#.

    • Answer: Operator overloading allows you to redefine the behavior of operators (like +, -, *) for custom types.

37. What are some common .NET libraries you've used?

    • Answer: (List common libraries like System.Data, System.Net, System.IO, etc. Tailor to your experience)

38. How do you handle null values in C#?

    • Answer: Null checks, null-conditional operator (`?.`), null-coalescing operator (`??`), and the Null-Object pattern.

39. What are some common debugging techniques you use?

    • Answer: Breakpoints, stepping through code, using the debugger's watch window, logging.

40. How do you handle memory management in C#?

    • Answer: Relying on garbage collection, disposing of IDisposable objects, using appropriate data structures.

41. Describe your experience with unit testing.

    • Answer: (Describe experience with frameworks like NUnit, MSTest, xUnit, and best practices)

42. What is your experience with version control systems (e.g., Git)?

    • Answer: (Describe experience with Git commands, branching strategies, and collaborative workflows)

43. How do you stay up-to-date with the latest C# features and technologies?

    • Answer: (Mention resources like Microsoft documentation, blogs, conferences, online courses)

44. Describe a challenging C# project you worked on and how you overcame the challenges.

    • Answer: (Describe a specific project, highlighting technical challenges and the solutions implemented)

45. What are your preferred coding practices and style guidelines?

    • Answer: (Mention coding style guides followed, such as naming conventions, commenting, and code organization)

46. Explain your experience with design patterns in C#. Give examples of when you used them.

    • Answer: (Describe specific design patterns used and their context in past projects)

47. How familiar are you with different database technologies?

    • Answer: (Mention databases like SQL Server, MySQL, PostgreSQL, and relevant experience with ORMs like Entity Framework)

48. How do you approach debugging performance issues in C# applications?

    • Answer: (Mention profiling tools, analyzing code execution, identifying bottlenecks)

49. Explain your understanding of SOLID principles.

    • Answer: (Describe each principle: Single Responsibility, Open/Closed, Liskov Substitution, Interface Segregation, Dependency Inversion)

50. What are your experiences with different architectural patterns (e.g., MVC, MVVM)?

    • Answer: (Describe experience with different architectural patterns and their applications)

51. How do you handle errors and exceptions in a production environment?

    • Answer: (Mention logging, error monitoring, exception handling strategies, and alerting)

52. What is your experience with asynchronous programming patterns beyond `async`/`await`?

    • Answer: (Mention other patterns like TAP, async/await with callbacks, and their application scenarios)

53. How familiar are you with different testing methodologies (e.g., TDD, BDD)?

    • Answer: (Describe familiarity and experience with different testing approaches)

54. What is your experience with performance optimization techniques in C#?

    • Answer: (Mention techniques like caching, efficient algorithms, code refactoring for performance)

55. Describe your experience working with RESTful APIs.

    • Answer: (Describe experience with creating, consuming, and testing REST APIs)

56. What is your experience with message queues (e.g., RabbitMQ, Azure Service Bus)?

    • Answer: (Describe experience with message queues, including scenarios where they were used)

57. What are your experiences with different deployment strategies?

    • Answer: (Mention deployment strategies like continuous integration/continuous deployment (CI/CD), various deployment environments)

58. How familiar are you with cloud platforms (e.g., Azure, AWS, GCP)?

    • Answer: (Mention specific cloud platforms and services used, and any relevant certifications)

59. What are your salary expectations?

    • Answer: (Provide a salary range based on research and experience)

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