Top 25 Interview Questions on C# Language Framework for 2025
C# (C-Sharp) is one of the most popular and versatile programming languages developed by Microsoft. As part of the .NET framework, C# is used to build a wide range of applications, from web and desktop to mobile apps. Whether you’re preparing for an interview or aiming to deepen your knowledge, understanding key C# concepts will give you a competitive edge. Here are the Top 25 Interview Questions on C# Language Framework for 2025 to help you succeed in your next interview.
1. What is C#?
Answer:
C# is an object-oriented, type-safe, and modern programming language developed by Microsoft as part of the .NET framework. It is used for building a wide variety of applications such as desktop applications, web applications, mobile apps, and games using the Unity engine.
2. What are the main features of C#?
Answer:
Some key features of C# include:
- Object-Oriented: Supports encapsulation, inheritance, and polymorphism.
- Type-Safety: Ensures that data types are strictly defined.
- Garbage Collection: Automatic memory management.
- LINQ (Language Integrated Query): Enables querying of data in a natural way.
- Cross-platform: Works with .NET Core for cross-platform development.
3. What is the difference between C# and C++?
Answer:
- C# is a high-level language designed for ease of use, automatic memory management, and safety. It works primarily with .NET applications.
- C++ is a lower-level language, giving developers more control over memory and hardware, and is commonly used for system-level programming, applications requiring high performance, and game development.
4. What is the CLR in C#?
Answer:
The Common Language Runtime (CLR) is the runtime environment for executing C# code. It provides important services such as memory management, exception handling, garbage collection, and security, allowing C# code to run on any platform with the .NET Framework.
5. What is the difference between == and Equals() in C#?
Answer:
==is a comparison operator that checks whether two variables point to the same object or have the same value (for primitive types).Equals()is a method that checks for logical equality. It compares the actual contents or state of the objects, not just their reference or memory location.
6. What are Value Types and Reference Types in C#?
Answer:
- Value Types: Contain data directly and are stored on the stack (e.g.,
int,float,bool). - Reference Types: Contain a reference (memory address) to the data and are stored on the heap (e.g.,
string,arrays, and user-defined objects).
7. What is an Exception in C#?
Answer:
An exception is an error that occurs during the execution of a program. C# provides structured exception handling through try, catch, and finally blocks to catch and handle errors effectively.
8. What is the using keyword in C#?
Answer:
The using keyword has two primary purposes:
- Namespace Declaration: It simplifies the use of classes from specific namespaces (e.g.,
using System;). - Resource Management: It defines a scope for objects that implement
IDisposableto ensure proper resource cleanup when the object goes out of scope.
9. What is the difference between ref and out in C#?
Answer:
ref: Allows passing a parameter by reference. The parameter must be initialized before being passed.out: Used for returning multiple values from a method. The parameter does not need to be initialized before passing, but it must be assigned a value before returning from the method.
10. What are Delegates in C#?
Answer:
A delegate is a type that represents references to methods with a specific parameter list and return type. It allows methods to be passed as parameters, making it useful for implementing event handling and callback mechanisms.
11. What is the async and await in C#?
Answer:
async: Defines an asynchronous method that can perform non-blocking operations.await: Used to wait for the completion of an asynchronous operation without blocking the main thread.
12. What is the purpose of the static keyword in C#?
Answer:
The static keyword defines class-level members that are shared across all instances of the class. A static member can be accessed without creating an instance of the class, and it exists for the lifetime of the application.
13. What is the difference between an abstract class and an interface in C#?
Answer:
- Abstract Class: Can have both abstract methods (without implementation) and concrete methods (with implementation). It can also have fields and constructors.
- Interface: Can only define method signatures and properties (without implementation). A class can implement multiple interfaces but can only inherit one abstract class.
14. What is Polymorphism in C#?
Answer:
Polymorphism allows methods to be used in different ways depending on the object they are acting upon. This can be achieved through method overloading (same method name, different parameters) and method overriding (replacing a base class method in a derived class).
15. What is the difference between Array and ArrayList in C#?
Answer:
- Array: A fixed-size collection of elements of the same type.
- ArrayList: A non-generic collection that can store elements of any data type and can dynamically resize.
16. What are Generics in C#?
Answer:
Generics allow for the creation of classes, methods, and interfaces with a placeholder for data types. This provides type safety and eliminates the need for type casting, making the code more reusable and easier to maintain.
17. What is LINQ in C#?
Answer:
LINQ (Language Integrated Query) is a feature in C# that allows querying of data from different data sources (arrays, collections, databases, XML) in a declarative manner using query syntax or method syntax.
18. What is the difference between is and as in C#?
Answer:
is: Checks if an object is compatible with a given type and returns a boolean value.as: Tries to cast an object to a specified type and returnsnullif the cast fails.
19. What is a Constructor in C#?
Answer:
A constructor is a special method used to initialize objects when they are created. It has the same name as the class and does not return any value. It can be overloaded to accept different parameters.
20. What are the different types of Collections in C#?
Answer:
C# provides several types of collections:
- Arrays: Fixed-size collections.
- List: A generic, dynamic collection.
- Dictionary<TKey, TValue>: A collection of key-value pairs.
- Queue: FIFO (First In, First Out) collection.
- Stack: LIFO (Last In, First Out) collection.
21. What is the null keyword in C#?
Answer:
The null keyword represents the absence of any object reference. It can be assigned to reference types (e.g., objects, arrays, etc.) to indicate that they do not point to any instance.
22. What is the difference between String and StringBuilder in C#?
Answer:
- String: Immutable, meaning once created, its content cannot be changed.
- StringBuilder: Mutable, allowing modification of strings without creating new objects, making it more efficient when performing multiple string operations.
23. What is a Singleton Pattern in C#?
Answer:
The Singleton Pattern ensures that a class has only one instance and provides a global point of access to that instance. It is commonly used for managing resources like database connections or configurations.
24. What is the difference between virtual and override in C#?
Answer:
virtual: Defines a method in the base class that can be overridden by derived classes.override: Provides a new implementation for a method that is marked asvirtualin a base class.
25. What are Events in C#?
Answer:
An event is a mechanism in C# that allows an object to notify other objects when something has occurred. Events are based on delegates and are commonly used in event-driven programming to handle user actions like button clicks or key presses.
Conclusion
By understanding the Top 25 Interview Questions on C# Language Framework for 2025, you’ll be better prepared to tackle any C# interview. This knowledge will not only help you demonstrate your expertise in C# but also give you an edge in landing your next job.
Good luck with your C# interview preparation!