Top C# .NET Interview Questions and Answers: A Comprehensive Guide

Securing a job as a C# .NET developer requires thorough preparation, not just in coding but also in understanding key concepts and being able to articulate them clearly during an interview. Here are some of the most common interview questions and answers, complete with examples, to help you get ready.

1. What is the difference between abstract class and interface in C#?

Answer:

An abstract class is a class that cannot be instantiated and is typically used as a base class. It can have abstract methods (methods without implementation) as well as concrete methods (methods with implementation).

An interface, on the other hand, can only have method declarations (without implementations) and properties. A class or struct that implements an interface must implement all its members.

Example:

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

Answer:

The using statement is used to ensure that IDisposable objects, such as files or database connections, are disposed of properly. It ensures that the Dispose method is called even if an exception occurs.

Example:

3. Explain the difference between StringBuilder and String in C#.

Answer:

String is immutable, meaning once created, its value cannot be changed. Each modification of a String results in the creation of a new string, which can be inefficient.

StringBuilder is mutable, allowing modification without creating new instances. It is more efficient for frequent modifications.

Example:

4. What are delegates and events in C#?

Answer:

A delegate is a type that represents references to methods with a particular parameter list and return type. Delegates are used to pass methods as arguments to other methods.

An event is a message sent by an object to signal the occurrence of an action. Events are based on delegates and are used to provide notifications.

Example:

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

Answer:

LINQ (Language Integrated Query) is a set of features in C# that adds query capabilities to the language syntax, enabling data querying directly within C#. LINQ can be used with collections, databases, XML, and more.

Example:

6. Explain the concept of asynchronous programming in C#.

Answer:

Asynchronous programming allows operations to run in the background while the application continues to respond to user actions or other events. In C#, this is achieved using the async and await keywords.

Example:

7. What is dependency injection and how is it implemented in C#?

Answer:

Dependency injection is a design pattern used to implement IoC (Inversion of Control), allowing a class to receive its dependencies from an external source rather than creating them itself. This enhances testability and maintainability.

Example:

8. What are the types of exceptions in C# and how to handle them?

Answer:

Exceptions in C# are categorized into system exceptions and application exceptions. Common types include System.Exception, System.IO.IOException, System.IndexOutOfRangeException, System.NullReferenceException, and custom exceptions.

Handling Exceptions Example: