C# Interview Question

Here you get a free C# Interview Question which helps you to Give Correct Answer of the Question in the Interview. It also helps you for you college exams Preparation.

Basics C# and Syntax

1. What is the difference between const, readonly, and static in C#? Provide examples.
2. Explain the purpose of nullable value types in C#. How are they declared and used?
3. What are extension methods in C#? Provide an example of when and how you would use one.
4. Discuss the var keyword. When should it be used, and when should it be avoided?
5. Explain the difference between String and string in C#. Are they interchangeable?
6. Why is Main declared static in C#, and what would happen if it weren’t?
7. Explain the role of partial classes in C#. How do they improve modularity?
8. What is the nameof operator, and how is it useful in C#?
9. Explain is and as operators in C# with practical examples.
10. Discuss how discard variables (_) can be used in C#.

Object-Oriented Programming (OOP)

1. Explain how C# implements polymorphism. Provide code examples.
2. What is the difference between method hiding (new keyword) and method overriding (override keyword)?
3. Discuss the concept of sealed classes and methods. Why and when would you use them?
4. Explain abstract classes versus interfaces. When should you choose one over the other?
5. How does C# handle multiple interface inheritance? Provide examples of resolving conflicts.
6. Can you declare a constructor in an interface? Why or why not?
7. How does C# support encapsulation? Provide examples demonstrating access modifiers.
8. What is the difference between shallow copy and deep copy in C#? Provide code examples.
9. Explain covariance and contravariance in delegates and generics with examples.
10. How do base and this keywords differ in usage?
11. Describe the purpose of virtual methods. What happens if a derived class doesn’t override them?
12. What are the pros and cons of implementing default interface methods in C#?
13. What is the difference between composition and inheritance? When is each appropriate?
14. Can static methods be overridden in C#? Why or why not?
15. Explain Object.Equals and Object.ReferenceEquals. How do they differ?
16. What is the difference between overriding and overloading? Provide examples.
17. Can you instantiate an abstract class in C#? If yes, how?
18. What is the purpose of a destructor in C#, and how is it declared?
19. Explain the concept of a “pure” virtual function in C#.
20. Why would you use protected internal as an access modifier?

LINQ and Collections

1. Explain deferred execution in LINQ. How does it affect query performance?
2. What is the difference between IEnumerable, IQueryable, and List in C#?
3. How would you write a custom LINQ extension method?
4. Discuss the significance of GroupBy in LINQ.
5. Provide a practical example. Explain the difference between Select and SelectMany.
6. What is the purpose of ToLookup in LINQ?
7. How does it differ from GroupBy?
8. How does LINQ-to-SQL differ from LINQ-to-Objects?
9. Provide an example of using LINQ to calculate the Cartesian product of two sequences.
10. Explain how LINQ uses lambda expressions for query syntax.How would you perform pagination using LINQ?
11. What are immutable collections in C#? How do they differ from regular collections?
12. Discuss the differences between HashSet, Dictionary, and List.
13. How does a ConcurrentDictionary differ from a regular Dictionary in C#?
14. What is the purpose of the yield keyword? How does it work in LINQ queries?
15. How does LINQ handle null values in sequences?
16. Explain how LINQ queries can be parallelized using PLINQ.
17. How does OrderBy preserve stability in sorting?
18. What are the advantages of using ObservableCollection over List?
19. Can LINQ queries be chained? Provide examples.
20. How does Aggregate work in LINQ? Provide practical usage scenarios.

Multithreading and Asynchronous Programming

1. Explain the difference between Task and Thread in C#.
2. How does async/await improve asynchronous programming in C#?
3. What is the difference between Task.Run and Task.Factory.StartNew?
4. How does the SynchronizationContext affect async code execution?
5. Explain the difference between lock, Monitor, and Mutex.
6. What is the purpose of async void, and why should it be avoided in most cases?
7. Explain the ThreadPool in C#. When should you use it?
8. What is a SemaphoreSlim, and how does it differ from Semaphore?
9. What is the role of ConfigureAwait(false) in async programming?
10. How do you implement a producer-consumer problem in C#?
11. What is the purpose of CancellationToken in async tasks? Provide examples.
12. Discuss the purpose of Task.WhenAll and Task.WhenAny.
13. How does the Parallel.ForEach method differ from ForEach?
14. What is a deadlock, and how can you prevent it in C#?
15. Explain the concept of thread safety and how to achieve it.
16. What is a BlockingCollection, and when would you use it?
17. How does the Volatile keyword work in C#?
18. Explain the difference between race conditions and data corruption in multithreading.
19. What is ConcurrentBag, and how does it work?
20. How do you ensure a task runs synchronously without blocking a thread?

Methods and Functions

1. What is the difference between params and params object[] in method parameters? Provide examples of their usage.
2. Can you declare two methods with the same name but different return types? Why or why not?
3. Explain the purpose of optional parameters in C#. How do they affect method overloading?
4. How do named arguments in C# improve method readability? Provide an example.
5. Explain how method hiding (new keyword) differs from overriding (override keyword) in C#. Provide examples.
6. Can a method be overridden in a derived class if it is declared as private in the base class? Why or why not?
7. What is a virtual method? How does the runtime decide which version of the method to call?
8. How do anonymous methods differ from lambda expressions in C#? Provide examples.
9. What is the role of Func, Action, and Predicate in method delegates? How are they used?
10. Explain how closures work with lambda expressions in methods. Provide examples of potential pitfalls.
11. How are extension methods resolved when multiple classes define the same extension method for the same type?
12. Can an extension method be used to override an existing instance method? Why or why not?
13. Write an extension method for a string to reverse its characters.
14. How does the async modifier affect the method signature and return type in C#?
15. Why can’t async methods return void, and what are the exceptions to this rule?
16. What happens if you call an async method without await?
17. Explain the differences between in, ref, and out parameters. Provide examples of each.
18. What is the purpose of default literal in generic methods, and how does it differ from default(T)?
19. How do you handle a method that takes a varying number of generic parameters?
20. How do you implement a method with a callback mechanism? Provide an example.