C# Interview Questions

C# (C-Sharp) is a powerful and flexible programming language developed by Microsoft that is highly popular in the world of software development. It is used for developing both desktop applications and web-based solutions, and is indispensable for those developing on the .NET platform. In C# interviews, candidates are assessed on their knowledge of the language’s basic and advanced features, their understanding of algorithms, and their problem-solving abilities. In this article, we’ll guide you through commonly asked C# interview questions and answers.

1. What is C# and What is it Used For?

C# is an object-oriented programming language developed by Microsoft. It runs on .NET Framework and .NET Core and is widely used especially on the Windows platform. It is also preferred in many fields such as game development, web development, and desktop applications.

When answering this question, it is important to emphasize C#’s role in the .NET ecosystem, its flexible structure, and wide range of uses.

2. What is Object-Oriented Programming (OOP)?

OOP is an approach in software development that enhances code reusability, maintainability, and manageability. The core concepts of OOP are:

• Encapsulation: Bundling data and methods within a class.
• Inheritance: Allowing one class to inherit features from another.
• Polymorphism: Allowing different classes to use the same method name with different implementations.
• Abstraction: Focusing only on essential information while hiding the unnecessary details.

Understanding OOP is fundamental when developing with C# and provides a strong advantage in interviews.

3. What is the Difference Between Value Types and Reference Types?

In C#, data types are divided into two main categories: Value Types and Reference Types.

• Value Types: Store data directly in memory. Examples include int, char, and bool. These types are stored in the stack.
• Reference Types: Store the address of the data, pointing to where it is located. Examples include class, string, and array. These are stored in the heap.

It is useful to mention the memory management role of these types when answering this question.

4. What are the Differences Between Abstract Classes and Interfaces?

This is another commonly asked question in C# interviews. Both abstract classes and interfaces provide abstraction, but they serve different purposes.

• Abstract Class: Can contain both abstract and non-abstract methods. A class can only inherit from one abstract class.
• Interface: Contains only method signatures and provides no implementation. A class can implement multiple interfaces.

Explaining when and why to use each is key to effectively answering this question.

5. What is Garbage Collection and How Does it Work in C#?

Garbage Collection in C# is a mechanism that automatically cleans up unused objects and memory that is no longer accessible. This prevents memory leaks and helps programs run more efficiently.

Understanding how Garbage Collection works is a big plus in terms of optimizing software performance.

6. What are async and await Keywords Used For?

Introduced in C# 5.0, async and await enable asynchronous programming. This prevents applications from freezing during long-running operations (like downloading a file) and provides a more responsive user experience.

Be sure to mention asynchronous tasks and task-based programming when answering this question.

7. How is the try-catch-finally Block Used?

In C#, the try-catch-finally block is used for error handling. The try block contains the code to be executed, the catch block handles specific exceptions, and the finally block executes code regardless of whether an error occurred.

Error handling is frequently tested in interviews, so it’s helpful to present a structured approach.

8. What are Lambda Expressions in C#?

Lambda expressions are shorthand for anonymous methods in C#. They are commonly used in LINQ queries and operations on collections. A typical lambda expression looks like this:

(x, y) => x + y;

Providing an example helps demonstrate your competency.

9. What is LINQ (Language Integrated Query)?

LINQ allows querying of data sources within C#. With LINQ, the same query syntax can be used on arrays, lists, XML, databases, etc. Here's an example:

var result = from s in students  
            where s.Age > 18  
            select s;

LINQ is often asked in interviews and is key for assessing data manipulation skills.

10. What are Delegates and When are They Used?

Delegates in C# are object-oriented references to methods. In other words, they allow a method to be passed as a parameter. They are commonly used in event handling and callback mechanisms.

When answering this question, it’s important to explain how delegates help make the program structure more flexible.

C# interview questions are designed to test a candidate’s understanding of the language’s core features, object-oriented principles, and overall coding skills. The above questions and answers will help you gain insight into what to expect during an interview and how to prepare effectively.

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