C# Interview Questions and Answers for experienced

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 usually compares references, unless overridden. For value types, it compares values.

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

   • Answer: C#'s garbage collector (GC) automatically reclaims memory occupied by objects that are no longer reachable. It operates non-deterministically, periodically identifying and freeing unused memory. This helps prevent memory leaks but introduces potential performance implications if not managed properly.

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

   • Answer: Delegates are type-safe function pointers. They allow you to pass methods as arguments to other methods. Events are a mechanism for broadcasting notifications. They use delegates under the hood. Example: A button click event uses a delegate to subscribe to a method that handles the click.

4. What is LINQ and how does it work?

   • Answer: LINQ (Language Integrated Query) is a set of technologies based on the idea of querying data from various sources (databases, XML, objects) using a common syntax. It uses extension methods to add query capabilities to existing collections. It translates queries into efficient operations behind the scenes.

5. Explain the difference between `ref` and `out` parameters.

   • Answer: `ref` parameters require the argument to be initialized before passing to the method. `out` parameters do not require initialization; the method is responsible for assigning a value. Both allow modifying the original variable within the called method.

6. What are Generics in C#? What are their benefits?

   • Answer: Generics allow you to write type-safe code that can work with various data types without losing type information. Benefits include type safety, performance improvements (no boxing/unboxing), and code reusability.

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

   • Answer: `async` and `await` keywords enable asynchronous programming, making it easier to write code that performs long-running operations without blocking the main thread. `async` marks a method as asynchronous, and `await` pauses execution until an asynchronous operation completes.

8. What are different ways to handle exceptions in C#?

   • Answer: Use `try-catch-finally` blocks to handle exceptions. `try` contains code that might throw exceptions, `catch` handles specific exception types, and `finally` executes regardless of whether an exception occurred. Custom exception classes can also be created.

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

   • Answer: Classes are reference types; structs are value types. Classes are allocated on the heap; structs are allocated on the stack. Structs are generally lighter weight for smaller data structures.

10. Explain the concept of polymorphism in C#.

    • Answer: Polymorphism allows objects of different classes to be treated as objects of a common type. This is achieved through inheritance and interfaces, enabling flexibility and extensibility.

11. Describe the different types of access modifiers in C#.

    • Answer: C# offers several access modifiers controlling the visibility and accessibility of members: `public`, `private`, `protected`, `internal`, `protected internal`.

12. What are interfaces in C# and how are they used?

    • Answer: Interfaces define a contract that classes must implement. They specify methods, properties, and events without providing implementation details, enabling polymorphism and loose coupling.

13. Explain the concept of inheritance in C#.

    • Answer: Inheritance allows a class (derived class) to inherit members (fields, methods, properties) from another class (base class). It promotes code reusability and establishes an "is-a" relationship.

14. What is a property in C#? How is it different from a field?

    • Answer: A property provides controlled access to a field. It encapsulates the data and can include logic for getting and setting values, ensuring data integrity.

15. What are indexers in C#? Give an example.

    • Answer: Indexers allow you to access elements of a class or struct using array-like syntax. They provide a way to expose internal data collections with custom indexing logic.

16. Explain the difference between boxing and unboxing in C#.

    • Answer: Boxing converts a value type to a reference type (Object). Unboxing converts a reference type (Object) back to its original value type. This process incurs performance overhead.

17. What are extension methods in C#?

    • Answer: Extension methods allow you to add new methods to existing types without modifying their original code. They are declared as static methods within a static class, and the first parameter specifies the type being extended (using the `this` keyword).

18. What are anonymous methods and lambda expressions?

    • Answer: Anonymous methods provide a way to create methods without a name, useful for delegates. Lambda expressions are more concise ways to define anonymous methods, using a => to separate input parameters from the expression.

19. Explain the concept of SOLID principles in object-oriented programming.

    • Answer: SOLID principles are a set of five design principles intended to make software designs more understandable, flexible, and maintainable. They are: Single Responsibility, Open/Closed, Liskov Substitution, Interface Segregation, and Dependency Inversion.

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