Top 10 C# Developer Interview Questions & Answers in 2024

1. Explain the differences between value types and reference types in C#.

Value types store their data directly, while reference types store a reference to the location of the data. Value types include simple types like int and float, and they are stored on the stack. Reference types, like classes and interfaces, are stored on the heap, and variables hold references to their locations.

2. Discuss the purpose and use of delegates in C#.

Delegates are type-safe function pointers used to reference methods with a specific signature. They enable event handling, callback mechanisms, and implementing generic algorithms. A delegate declaration includes the return type and parameters, providing a level of abstraction for method calls.

3. Explain the role of the 'async' and 'await' keywords in C#.

'async' and 'await' are used for asynchronous programming in C#. 'async' designates a method as asynchronous, allowing the use of 'await' inside it. 'await' pauses the method execution until the awaited task completes, freeing up the thread for other tasks.

4. Describe the differences between 'IEnumerable' and 'IQueryable' in LINQ.

'IEnumerable' is an in-memory collection interface suitable for querying data in memory, such as arrays and lists. 'IQueryable' extends 'IEnumerable' and is used for querying external data sources, like databases. 'IQueryable' enables deferred execution, optimizing queries for the underlying data store.

5. Explore the 'Dependency Injection' pattern in C#. How is it implemented, and what are its advantages?

Dependency Injection (DI) is a design pattern where dependencies are injected into a class rather than created within it. It improves modularity, testability, and flexibility. DI is commonly implemented using constructor injection, method injection, or property injection. Popular DI frameworks in C# include Microsoft.Extensions.DependencyInjection and Autofac.

6. Discuss the benefits of using the 'using' statement in C#.

The 'using' statement is used for resource management, ensuring that IDisposable objects are properly disposed of when they go out of scope. It reduces memory leaks and enhances code readability. 'using' is commonly employed with database connections, file streams, and other resource-intensive objects.

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

'String' is immutable, meaning once created, its content cannot be changed. 'StringBuilder' is mutable and allows efficient modifications of its content, making it more suitable for scenarios involving frequent string manipulations. 'StringBuilder' is preferable for concatenating multiple strings.

8. Describe the 'async/await' best practices in C#.

Best practices for 'async/await' include avoiding 'async void' methods, using 'ConfigureAwait(false)' to prevent deadlocks, and preferring 'Task.Run' for CPU-bound operations. Proper exception handling, cancellation support, and understanding the synchronization context are crucial for efficient asynchronous programming.

9. Discuss the use of attributes in C# and provide an example of a scenario where custom attributes are beneficial.

Attributes in C# provide metadata that can be added to code elements. Custom attributes are user-defined metadata. For example, creating a custom attribute to mark methods that should be logged allows developers to annotate methods with additional information, improving code documentation and maintainability.

10. Explain the concept of 'boxing' and 'unboxing' in C#.

'Boxing' is the process of converting a value type to a reference type, usually to store it in a collection or pass it as an object. 'Unboxing' is the reverse process, extracting the value type from the object. Boxing and unboxing incur performance overhead, and developers should be mindful of their usage in performance-critical scenarios.