C# Interview Questions and Answers for 2 years experience

1. What is the difference between `==` and `Equals()` in C#?

   • Answer: `==` compares references for reference types and values for value types. `Equals()` is a method that can be overridden to provide custom comparison logic. For reference types, it typically compares references unless overridden. For value types, it compares values. In short, `==` checks for equality at the memory address level, while `Equals()` checks for equality of the object's content.

2. Explain the concept of value types and reference types in C#.

   • Answer: Value types (like `int`, `float`, `struct`) store their data directly on the stack. When you assign a value type variable to another, a copy of the data is created. Reference types (like `class`, `string`) store a reference to the data on the heap. Assigning a reference type variable to another creates a copy of the reference, not the data itself. Both variables point to the same data in memory.

3. What is garbage collection in C#?

   • Answer: Garbage collection is an automatic memory management process in C#. The .NET runtime automatically reclaims memory occupied by objects that are no longer reachable by the program. This prevents memory leaks and simplifies memory management for developers.

4. What are delegates and events in C#?

   • Answer: Delegates are type-safe function pointers. They allow you to encapsulate methods and pass them as arguments to other methods. Events use delegates to provide a mechanism for objects to notify other objects about significant occurrences. Events follow a publisher-subscriber pattern where one object (publisher) raises an event, and other objects (subscribers) can register to receive notifications.

5. Explain the difference between `string` and `StringBuilder` in C#.

   • Answer: `string` is an immutable type. Every time you modify a string, a new string object is created. `StringBuilder` is a mutable type, designed for efficient string manipulation, especially when concatenating many strings. Using `StringBuilder` avoids the overhead of repeatedly creating new string objects.

6. What is LINQ (Language Integrated Query)? Give an example.

   • Answer: LINQ allows you to write queries against various data sources (databases, XML, collections) using C# syntax. Example: `var evenNumbers = numbers.Where(n => n % 2 == 0);` This query filters a collection `numbers` to return only even numbers.

7. What are properties in C#?

   • Answer: Properties provide a way to access and modify the internal state of an object without directly exposing the internal fields. They typically consist of a `get` accessor (to retrieve the value) and a `set` accessor (to modify the value). They encapsulate data and allow for validation and other actions before setting or getting the value.

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

   • Answer: Polymorphism allows objects of different classes to be treated as objects of a common type. This is often achieved through inheritance and virtual/override methods. Example: A base class `Animal` has a virtual method `MakeSound()`. Derived classes like `Dog` and `Cat` override this method to provide specific implementations. You can then have an array of `Animal` objects containing `Dog` and `Cat` instances, and call `MakeSound()` on each, getting the appropriate sound.

9. Explain inheritance in C#.

   • Answer: Inheritance is a mechanism where a new class (derived class) inherits properties and methods from an existing class (base class). This promotes code reusability and establishes an "is-a" relationship between classes. The derived class can extend and override the functionality of the base class.

10. What is the difference between `abstract` and `virtual` methods?

    • Answer: `abstract` methods are declared without implementation. They must be implemented by derived classes. `virtual` methods have an implementation in the base class but can be overridden by derived classes. An abstract class cannot be instantiated, whereas a class with virtual methods can.

11. What are interfaces in C#?

    • Answer: Interfaces define a contract that classes can implement. They specify a set of methods, properties, and events that a class must provide. Interfaces promote polymorphism and decoupling.

12. What is exception handling in C#? Explain `try`, `catch`, and `finally` blocks.

    • Answer: Exception handling is a mechanism to gracefully handle runtime errors. The `try` block contains code that might throw an exception. The `catch` block handles specific exceptions. The `finally` block contains code that is always executed, regardless of whether an exception occurred, often used for cleanup.

13. What are generics in C#?

    • Answer: Generics allow you to write type-safe code that can work with different data types without sacrificing type safety. They use type parameters to create reusable components that can be instantiated with specific types at compile time.

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

    • Answer: Asynchronous programming allows you to perform long-running operations without blocking the main thread. `async` indicates an asynchronous method. `await` pauses execution of the method until the awaited task completes, without blocking the thread.

15. What are some common design patterns in C#? Give examples.

    • Answer: Common design patterns include Singleton (ensures only one instance of a class), Factory (creates objects without specifying the exact class), Observer (defines a one-to-many dependency between objects), MVC (Model-View-Controller for separating concerns in applications).

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

    • Answer: Use null checks (`if (object != null)`), the null-conditional operator (`?.`), the null-coalescing operator (`??`), and the null-coalescing assignment operator (`??=`). The C# 8 and later versions also introduce nullable reference types to enhance null safety.

17. What are extension methods in C#?

    • Answer: Extension methods allow you to add new methods to existing types without modifying their source code. They are static methods declared in a static class, with the `this` keyword preceding the first parameter, which specifies the type being extended.

18. Explain the difference between a class and a struct in C#.

    • Answer: Classes are reference types, while structs are value types. Structs are typically used for small, simple data structures, while classes are used for more complex objects. Structs are allocated on the stack, while classes are allocated on the heap.

19. What is dependency injection?

    • Answer: Dependency injection is a design pattern where dependencies are provided to a class rather than created within the class. This improves testability, maintainability, and reusability.

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

    • Answer: The `using` statement ensures that disposable resources (like files, network connections, database connections) are properly closed even if exceptions occur. It calls the `Dispose()` method automatically.

21. Explain how to work with files and directories in C#.

    • Answer: Use the `System.IO` namespace. Classes like `File`, `Directory`, `StreamReader`, and `StreamWriter` provide methods for creating, reading, writing, and deleting files and directories.

22. How do you serialize and deserialize objects in C#?

    • Answer: Use serialization techniques like JSON serialization (using `Newtonsoft.Json` or built-in `System.Text.Json`), XML serialization, or binary serialization. Serialization converts an object into a stream of bytes, and deserialization reconstructs the object from the byte stream.

23. What are some ways to improve the performance of a C# application?

    • Answer: Use profiling tools to identify bottlenecks. Optimize algorithms, use appropriate data structures, minimize object allocations, use caching, and consider asynchronous operations for I/O-bound tasks.

24. Explain multithreading in C#.

    • Answer: Multithreading allows you to execute multiple parts of your program concurrently, improving performance, especially on multi-core processors. Use `Thread`, `Task`, or `async/await` for multithreading.

25. What is the difference between a `List` and an `Array` in C#?

    • Answer: `List` is a dynamic array that can grow or shrink as needed, while `Array` is a fixed-size collection. `List` provides more flexibility for adding and removing elements, while `Array` offers better performance for accessing elements by index.

26. What are some common .NET libraries you have used?

    • Answer: This will vary depending on experience, but might include `System.IO`, `System.Net`, `System.Data`, `System.Linq`, `System.Threading.Tasks`, `Newtonsoft.Json`, Entity Framework Core etc.

27. Describe your experience with database interactions in C#.

    • Answer: This should detail specific technologies used (e.g., ADO.NET, Entity Framework Core), database systems (e.g., SQL Server, MySQL, PostgreSQL), and types of interactions (e.g., CRUD operations, stored procedures).

28. How do you handle errors and exceptions in your code?

    • Answer: Describe the use of `try-catch-finally` blocks, logging exceptions, using appropriate exception types, and handling exceptions gracefully to prevent application crashes.

29. Explain your experience with unit testing in C#.

    • Answer: Describe the use of testing frameworks (e.g., NUnit, xUnit, MSTest), writing unit tests, mocking dependencies, and the importance of testable code.

30. What are your preferred debugging techniques?

    • Answer: Describe using the debugger (breakpoints, stepping through code), logging, using diagnostic tools, and analyzing error messages.

31. How do you stay up-to-date with the latest technologies and trends in C#?

    • Answer: Mention reading blogs, following industry news, attending conferences/meetups, taking online courses, experimenting with new technologies.

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

    • Answer: Provide a specific example, highlighting the challenges encountered, the solutions implemented, and the lessons learned.

33. Explain your experience with version control systems (like Git).

    • Answer: Describe your experience with Git (branching, merging, pull requests, resolving conflicts).

34. What is your understanding of SOLID principles?

    • Answer: Explain the five SOLID principles (Single Responsibility, Open/Closed, Liskov Substitution, Interface Segregation, Dependency Inversion) and how they improve code quality.

35. What is your experience with design patterns?

    • Answer: Mention specific design patterns you've used (e.g., Singleton, Factory, Observer, Strategy, Decorator) and explain how they were applied in your projects.

36. How do you handle conflicts in a team environment?

    • Answer: Describe your approach to resolving conflicts, emphasizing communication, collaboration, and finding mutually acceptable solutions.

37. Describe a time you had to debug a particularly complex issue. What steps did you take?

    • Answer: Give a detailed account, highlighting systematic problem-solving skills.

38. How do you approach learning new technologies?

    • Answer: Describe your learning style and resources used (documentation, online courses, tutorials, experimentation).

39. What are your strengths and weaknesses as a C# developer?

    • Answer: Be honest and provide specific examples. For weaknesses, focus on areas you are working to improve.

40. Where do you see yourself in 5 years?

    • Answer: Show ambition and career goals, aligning them with the company's opportunities.

41. Why are you interested in this position?

    • Answer: Demonstrate genuine interest in the company and the role, highlighting relevant skills and experience.

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