C# Programming Language Overview:

C# (pronounced "C sharp") is a modern, object-oriented programming language developed by Microsoft. It is part of the .NET framework and is widely used for building Windows applications, web applications, cloud services, and more. C# is known for its simplicity, type safety, and scalability, making it a versatile language for various software development scenarios.

Key Features of C#:

1. Object-Oriented: C# supports the principles of object-oriented programming (OOP), such as encapsulation, inheritance, and polymorphism.
2. Type Safety: C# is a statically-typed language, which means that the type of a variable is known at compile time, reducing the chances of runtime errors.
3. Memory Management: C# includes automatic memory management through a garbage collector, simplifying memory allocation and deallocation.
4. .NET Framework Integration: C# is tightly integrated with the .NET framework, providing access to a wide range of libraries and tools for application development.
5. Language Interoperability: C# can interoperate with other languages that target the Common Language Runtime (CLR), enabling integration with existing codebases.
6. Exception Handling: C# supports robust exception handling to manage errors and unexpected events in a structured way.
7. LINQ (Language-Integrated Query): LINQ allows developers to write queries directly in C# for querying data from various sources, such as databases and collections.
8. Asynchronous Programming: C# provides asynchronous programming features, such as async/await, to simplify the development of scalable and responsive applications.
9. Delegates and Events: C# supports delegates, allowing the creation of type-safe function pointers, and events for implementing the observer pattern.
10. Properties and Indexers: C# provides a convenient way to encapsulate fields through properties and indexers, promoting good coding practices.

20 Technical Interview Questions and Answers:

1. What is C# and what are its key features?

   Answer: C# is an object-oriented programming language developed by Microsoft. Key features include OOP support, type safety, automatic memory management, .NET framework integration, and language interoperability.

2. Explain the difference between value types and reference types in C#.

   Answer: Value types store their data directly, while reference types store a reference to the data. Value types are stored on the stack, and reference types are stored on the heap.

3. What is the purpose of the 'using' statement in C#?

   Answer: The 'using' statement is used for resource management, ensuring that IDisposable objects are properly disposed of after use.

4. Describe the differences between 'abstract' and 'interface' in C#.

   Answer: An abstract class can have abstract and non-abstract members, while an interface only contains abstract members. A class can inherit from only one abstract class, but it can implement multiple interfaces.

5. What is the role of the 'async' and 'await' keywords in C#?

   Answer: 'async' is used to define an asynchronous method, and 'await' is used to asynchronously wait for a task to complete without blocking the calling thread.

6. Explain the purpose of the garbage collector in C#.

   Answer: The garbage collector automatically manages memory by reclaiming unused objects, preventing memory leaks and simplifying memory management.

7. How does exception handling work in C#?

   Answer: Exception handling in C# is done using try, catch, and finally blocks. Exceptions are thrown using the 'throw' keyword and caught using catch blocks.

8. What is the role of delegates in C#?

   Answer: Delegates are type-safe function pointers used to define and encapsulate methods, enabling callback mechanisms and event handling.

9. Explain the concept of polymorphism in C#.

   Answer: Polymorphism allows objects of different types to be treated as objects of a common base type, enabling code reuse and flexibility.

10. What is LINQ, and how is it used in C#?

    Answer: LINQ (Language-Integrated Query) allows writing queries directly in C# to query data from various sources like databases and collections, providing a unified querying syntax.

11. Differentiate between 'readonly' and 'const' in C#?

    Answer: 'const' is compile-time constant, and 'readonly' is runtime constant. 'const' is implicitly static, while 'readonly' can be instance-specific.

12. Explain the 'yield' keyword in C#.

    Answer: 'yield' is used in iterator methods to pause execution and return control to the caller, allowing the method to produce a sequence of values lazily.

13. What are indexers in C#?

    Answer: Indexers allow objects to be indexed like arrays, enabling custom types to provide array-like access to their elements.

14. How does the 'using' statement work with IDisposable objects?

    Answer: The 'using' statement ensures that the Dispose method of IDisposable objects is called when leaving the scope, facilitating proper resource cleanup.

15. What is the purpose of the 'lock' statement in C#?

    Answer: The 'lock' statement is used to synchronize access to a shared resource in a multithreaded environment, preventing multiple threads from accessing the resource simultaneously.

16. How does dependency injection work in C#?

    Answer: Dependency injection is a design pattern where dependencies are injected into a class rather than created internally. It promotes loose coupling and testability.

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

    Answer: Boxing is the process of converting a value type to a reference type, and unboxing is the process of converting a boxed value type back to its original value type.

18. What is the purpose of the 'params' keyword in C#?

    Answer: The 'params' keyword allows a method to accept a variable number of parameters, simplifying method calls with varying argument counts.

19. How can you implement a Singleton pattern in C#?

    Answer: A common way is to use a private static instance and a private constructor to ensure only one instance is created and provide a public static method to access it.

20. Explain the differences between 'StringBuilder' and 'String' in C#.

    Answer: 'StringBuilder' is mutable and designed for efficient string manipulation, while 'String' is immutable and any modification results in a new string instance. 'StringBuilder' is more efficient for concatenating multiple strings.