Top 50 C# Basic Interview Questions and Answers (For Freshers & Experienced)
A complete collection of the 50 most important C# basic interview questions and answers, covering concepts like OOP, classes, interfaces, data types, collections, exception handling, and .NET fundamentals. Ideal for quick revision before interviews.
1. What is C#?
C# is a modern, object-oriented programming language developed by Microsoft for .NET applications like web, desktop, mobile, and cloud.
2. What is .NET Framework?
A software framework providing libraries, runtime (CLR), and tools to build applications.
3. What is CLR?
Common Language Runtime executes .NET code and manages memory, exceptions, security, and garbage collection.
4. What is CTS?
Common Type System defines how data types are declared and used across .NET languages.
5. What is CLS?
Common Language Specification ensures interoperability between different .NET languages.
6. What is a Class?
A blueprint for creating objects containing fields, methods, and properties.
7. What is an Object?
An instance of a class created using the new keyword.
8. What is a Namespace?
A container used to organize classes. Example: System.IO.
9. What is an Interface?
A contract that contains declarations but no implementations.
10. What is Inheritance?
A mechanism where one class acquires properties and methods of another class using : operator.
11. Types of Inheritance in C#?
- Single
- Multilevel
- Hierarchical
- Multiple (via interfaces)
12. What is Polymorphism?
Ability of a method to behave differently.
Types:
- Compile-time (Overloading)
- Run-time (Overriding)
13. What is Abstraction?
Hiding implementation and showing only necessary features using classes/interfaces.
14. What is Encapsulation?
Wrapping data and methods using access modifiers like private, public.
15. What are Access Modifiers in C#?
public, private, protected, internal, protected internal, private protected.
16. What is Method Overloading?
Methods with the same name but different parameters.
17. What is Method Overriding?
Redefining a base class method in the derived class using virtual and override.
18. What is Constructor?
A special method that initializes an object.
19. Types of Constructors?
- Default
- Parameterized
- Copy
- Static
- Private
20. What is Destructor?
A method that cleans resources: ~ClassName().
21. What is Static Keyword?
Used for members that belong to the class, not objects.
22. What is Sealed Class?
A sealed class cannot be inherited.
23. What is Abstract Class?
A class that cannot be instantiated and may contain abstract methods.
24. What is Boxing?
Converting value type → object type.
25. What is Unboxing?
Converting object type → value type.
26. What is Value Type?
Stored in stack. Example: int, float, bool, structs.
27. What is Reference Type?
Stored in heap. Example: class, interface, array, string.
28. What is Array in C#?
A collection of similar data types stored in continuous memory.
29. Types of Arrays?
- Single-dimensional
- Multi-dimensional
- Jagged array
30. Difference between Array & ArrayList?
| Array | ArrayList |
| Fixed size | Dynamic size |
| Stores single type | Stores any type |
| Fast | Slightly slower |
31. What is String?
An immutable sequence of characters.
32. What is StringBuilder?
A mutable string class used for frequent modifications.
33. What is Exception Handling?
Managing runtime errors using try, catch, finally, throw.
34. What is Custom Exception?
User-defined exception by inheriting Exception class.
35. What is Enumeration (enum)?
A value type containing named constants.
36. What is Struct?
A value type that can contain fields, methods, properties.
37. What is Difference Between Class and Struct?
| Class | Struct |
| Reference type | Value type |
| Supports inheritance | Does not |
| Slower | Faster |
38. What is Delegates?
A type-safe function pointer.
39. Types of Delegates?
- Single Delegate
- Multicast Delegate
- Func
- Action
- Predicate
40. What is Event?
A mechanism for communication between objects using delegates.
41. What is LINQ?
Language Integrated Query used to query collections and databases.
42. What is Anonymous Method?
Method without a name, created using delegate keyword.
43. What is Lambda Expression?
Short-hand function using =>.
Example: x => x * x
44. What is Extension Method?
A way to add methods to existing types without modifying them.
45. What is Partial Class?
A class split into multiple files using partial keyword.
46. What is Indexer?
Allows a class to be indexed like an array using this[].
47. What is Getter and Setter?
Used to read/write private variables through properties.
48. What is Thread?
A lightweight process used for parallel execution.
49. What is Async & Await?
Used for asynchronous programming to avoid blocking the main thread.
50. What is Garbage Collection?
Automatic memory management that removes unused objects.
