40 .Net Interview Questions and Answers (2025)

.NET Overview

Microsoft developed .NET, a free and open-source development platform. Professionals can use it to build various applications, including web, desktop, mobile, and cloud-based apps.

Developers use .NET because

• It supports multiple languages, like C#, VB.NET, COBOL, F#, Perl, etc
• It offers strong security
• It makes it easy to create high-performance applications
• It builds reliable and scalable software for businesses and enterprises

.NET Interview Questions for Beginners

This set of questions is helpful for beginners to kickstart their preparation.

1. What is .NET, and how does the .NET Framework work?

.NET is a Microsoft platform that develops web, desktop, and mobile applications.

• Code written in C#, F#, or VB
• Compiled into CIL
• Stored as .dll or .exe

The CLR uses JIT to convert CIL into machine code at runtime so it can run on any system architecture.

2. What are the major components of the .NET Framework?

The major components of the .NET Framework are:

1. CLR – Runs code and handles memory, security, and exceptions
2. FCL – Predefined methods and types (e.g., System.IO for file operations)
3. BCL – Core set of reusable classes
4. CTS – Defines how data types are handled across languages
5. CLS – Ensures language interoperability

3. What is an EXE and a DLL?

EXE or Executable is a file that runs a program. It is created when you build an app and cannot be reused by other apps.

DLL, or Dynamic Link Library, is a file with reusable code that other programs use. System.Data.dll is an example of a DLL used for database tasks.

4. What are the differences between CTS and CLS?

5. What is JIT?

JIT, or "Just In Time," is a compiler that, at runtime, transforms the compiled intermediate code (CIL) into machine code so that it may execute on the hardware of the computer. This enhances performance. This enhances performance. JIT compiles methods just before they are executed when a .NET app runs.

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6. What is a garbage collector?

The garbage collector is a virtual machine component that automatically manages memory allocation and deallocation. GC ensures that memory occupied by unused objects is reclaimed. So there are no memory leaks and improved application performance.

7. What is caching?

Storing data in a temporary location, like memory, prevents memory leaks and improves application performance. This is called caching. It helps to quickly access the data later instead of recalculating or fetching it again.

MemoryCache cache = MemoryCache.Default;
cache.Set("username", "John", DateTimeOffset.Now.AddMinutes(10));
string name = cache.Get("username") as string;  // Fast access

8. What is an assembly?

An assembly is a file (.exe or .dll) automatically created by the compiler in .NET. It contains code and resources that work together. It is used to run or share parts of a program.

9. What are the different types of assembly?

There are two types of assemblies:

1. Private Assembly – Used by one application only. It must be placed in that app’s folder.
2. Shared (Public) Assembly – Used by many applications. It’s stored in the Global Assembly Cache (GAC). You don't need to place the same assembly in every app’s folder. 

10. What is the difference between managed and unmanaged code?

11. What is Microsoft Intermediate Language?

Microsoft Intermediate Language (MSIL) is the low-level code generated by the .NET compiler from your source code. It includes instructions for loading, storing, method calls, and more. At runtime, the JIT compiler converts MSIL into native machine code that runs on your OS.

Example C# code:

Console.WriteLine("Hello");

12. How is ASP.NET different from .NET?

13. What is cross-page posting?

Cross-page posting happens when a form on one ASP.NET page posts data to a different page, not itself. This is done using the PostBackUrl property of a button.

14. What are the differences between value and reference types in .NET?

15. What is serialization and deserialization in .NET?

Serialization converts an object into a format (like JSON, XML, or binary) for storage or sending, while deserialization converts that data back into an object.

Example (JSON):

string json = JsonConvert.SerializeObject(obj);
// Serialization
MyClass obj2 = JsonConvert.DeserializeObject<MyClass>(json);
// Deserialization

.NET Interview Questions for Experienced Professionals

Are you an experienced professional who wants to brush up on the .NET concepts for your next interview? Here are the .NET interview questions for 5 years of experience:

16. Explain role-based security in .NET

Role-based security in .NET means giving users access based on their assigned roles (like Admin, User, Guest). It helps control what each user can do in an app.

17. What is the order of the events in a page life cycle?

These are the eight key events in the ASP.NET page life cycle. The events are executed in this order to render a page properly:

1. Page_PreInit – Set master page/theme
2. Page_Init – Initialize controls
3. Page_InitComplete – Initialization done
4. Page_PreLoad – Before Load event
5. Page_Load – Load data into controls
6. Page_LoadComplete – Page loading complete
7. Page_PreRender – Final changes before rendering
8. Render – Renders HTML to the browser.

18. What is the difference between int and Int32? 

There is no difference. In C#, int is just an alias for System.Int32. Both represent a 32-bit signed integer.

Example:

int a = 10;
System.Int32 b = 20;

19. What is localization and globalization?

Globalization is designing apps to support multiple cultures/languages. Localization is adapting the app to a specific culture (like translating it into Spanish). Some of them are changing dates, currency, or language format based on the region where the user is located.

20. What is MVC?

MVC stands for Model-View-Controller. It is a design pattern used in ASP.NET to build web apps by separating logic, UI, and user input handling. This separation makes code cleaner and easier to manage.

21. What is a delegate in .NET?

A delegate in .NET is like a pointer to a method. It holds a reference to a method with a specific signature. It can call that method and even pass it around like a variable. Delegates are also used to define custom events.

Example:

public delegate void MyDelegate(string msg);
void Show(string msg) => Console.WriteLine(msg);
MyDelegate del = Show;
del("Hello from delegate!");

22. What security controls are available on ASP.NET?

ASP.NET provides built-in security controls to manage login, authentication, and password recovery:

23. What is boxing and unboxing in .NET?

Boxing converts a value type (like int) into a reference type (object) automatically (implicitly).

Unboxing converts it back to a value type. It's manual (explicit).

Example:

int x = 10;
object obj = x;
// Boxing
int y = (int)obj;
// Unboxing

24. What is MIME in .NET?

MIME stands for Multipurpose Internet Mail Extension. It is a .NET standard that tells the browser or client what type of data is being sent. The data can be an image, audio, or PDF. MIME is used in email and web apps to define content types.

Example MIME types:

• text/html for HTML pages
• image/png for PNG images
• application/pdf for PDF files

25. What is the use of manifest in .NET?

A manifest in .NET is part of an assembly that stores metadata about the assembly. It contains:

• Assembly version info
• Scope of the assembly
• References to other assemblies/classes
• Security permissions

This helps the CLR manage and load assemblies correctly.

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26. What is the meaning of CAS in .NET?

CAS is Code Access Security. It is part of .NET's built-in security model and restricts what code can do in .NET based on where it came from or who runs it. CAS gives limited permissions to external or risky code to help protect the system, so there is no unauthorized access to resources.

27. What is the appSettings section in the web.config file?

The appSettings section in web.config stores user-defined key-value pairs (like config values) that can be used throughout the application.

Example:

<configuration>
<appSettings>
<add key="ConnectionString"value="server=local;pwd=password;database=default"/>
</appSettings>
</configuration>

Access in C#:

string conn=ConfigurationManager.AppSettings["ConnectionString"];

28. What are the types of memories supported in .NET?

In .NET, there are two types of memory used for managing data:

Stack:

• Stores value types (like int or float)
• Static memory allocation for method calls and local variables

Heap:

• Stores reference types (like objects)
• Dynamic memory allocation for data that needs to persist outside method calls

29. What are the parameters that control the connection pooling behaviors?

In .NET connection pooling, the following four parameters control its behavior:

• Connect Timeout: Specifies how long it takes for a connection to open before timing out
• Min Pool Size: Sets the minimum number of connections in the pool
• Max Pool Size: Sets the maximum number of connections allowed in the pool
• Pooling: Specifies whether connection pooling is enabled (true) or disabled (false)

30. What are MDI and SDI?

• MDI (Multiple Document Interface): Allows multiple child windows within a single parent window. Shared components like toolbars and menus are available across all child windows.
• SDI (Single Document Interface): Each document opens in its own separate window with its own set of components, like toolbars and menus. No parent-child relationship exists between Windows.

.NET Core Interview Questions

31. What is .NET Core, and what is it used for?

.NET Core is a cross-platform, open-source framework developed by Microsoft for building modern web, cloud, and IoT applications. It allows you to run applications on Windows, macOS, and Linux.

32. What are .NET Core Components?

.NET Core components are as follows:

• Runtime: The environment that runs .NET Core applications
• Libraries: A set of class libraries (like ASP.NET Core, Entity Framework Core) for building different types of apps
• SDK (Software Development Kit): Provides tools and libraries for building .NET Core applications
• CLI (Command-Line Interface): Tools for creating, building, and running .NET Core applications via the command line.

33. What is CoreCLR?

CoreCLR is the runtime execution engine for .NET Core. It includes:

• JIT (Just-In-Time) compiler for converting CIL into native code
• Garbage collector for memory management
• Low-level classes and primitive data types

CoreCLR enables cross-platform execution on Windows and Linux and supports languages like C# and VB.

34. What is CoreRT?

CoreRT is a native runtime for .NET that compiles applications ahead-of-time (AOT), unlike JIT-based runtimes. It is part of the .NET Native project.

• No JIT compiler: It compiles code ahead of time, reducing runtime overhead
• Supports RTTI and reflection: It still allows runtime type identification and reflection
• Efficient with unused code: Unused metadata and code are eliminated, which makes the application more optimized

35. What is the purpose of webHostBuilder()?

The WebHostBuilder() function configures and builds a web host for hosting an ASP.NET Core web application. It uses method chaining to set up the HTTP request pipeline and services (e.g., Use()). Build() creates the necessary services and returns an IWebHost to host the web application. It is part of Microsoft.AspNetCore.Hosting namespace.

36. What is Transfer-Encoding?

Transfer-Encoding is an HTTP header that specifies how the data is transferred between two nodes (e.g., client and server). It is hop-by-hop and is not applied directly to the resource itself. In Chunked Transfer-Encoding, data is sent in chunks, which is useful when the total size of the response is unknown before the request finishes. Each chunk is sent sequentially to the client.

37. What are Zero Garbage Collectors?

Zero Garbage Collectors prevent automatic memory management by not reclaiming unused memory.

Two main uses:

• Custom Garbage Collection: This allows you to create your memory management system
• Special Use Cases: This is ideal for short-lived applications or applications that do not allocate memory (Zero-alloc programming), where Garbage Collection overhead is unnecessary

38. What is CoreFx?

CoreFX is the set of class libraries for .NET Core that provides essential functionality like collections, console input/output, file systems, XML, JSON, async operations, and more. It is platform-neutral, can run across all platforms, and is implemented as a single portable assembly.

39. What is Explicit Compilation (Ahead Of Time compilation)?

AOT compilation compiles high-level code into low-level code during build time, reducing runtime workload and providing faster startup. It requires more memory and disk space but avoids expensive runtime actions like disk I/O. AOT compilation happens once during build time, making the app smaller and faster.

Example: In Angular, AOT compiles templates during build time for faster rendering:

ng build --prod --aot

40. What is the use of generating SQL scripts in .NET Core?

Generating SQL scripts in .NET Core helps debug or deploy migrations to a production database. These scripts can be reviewed for accuracy. This checks whether the data is correct and can be customized to meet production database requirements.

7 Tips to Prepare for a .NET Interview

Now that you have understood the 40 dot net interview questions and answers, it’s time to learn the tips for .NET interview preparation.

1. Master C# Basics

Have ample knowledge of the C# basics. C# syntax, data types, loops, conditions, and basic object-oriented programming (OOP) principles. Inheritance and polymorphism are the top things to cover.

2. Understand .NET Core and ASP.NET Core

You should be clear on the differences between .NET Core and .NET Framework. Learn all the basic differences between the two. You must understand how ASP.NET Core is used for web applications.

3. Learn Entity Framework Core

Be ready to discuss how to perform CRUD operations with EF Core, set up relationships, and understand concepts like migrations and LINQ queries.

4. Practice Unit Testing

Your familiarity with unit testing frameworks is essential. It is helpful if you know how to write unit tests, mock dependencies using Moq, and test for edge cases.

5. Know Dependency Injection (DI)

The concept of DI is also worth getting acquainted with. You must know how to implement it in .NET Core applications and improve maintainability and testability. 

6. Study Common Design Patterns

Do not forget to learn and practice common design patterns because they are often discussed in interviews.  The common ones include Singleton, Factory, Repository, and MVC.

7. Prepare for Problem-Solving Questions

Practice coding problems and algorithms on platforms like LeetCode or HackerRank to improve problem-solving skills and time management.

Conclusion

Learn the dotnet interview questions discussed in the article to tackle interviews and demonstrate proficiency in .NET development. You can take a step further to enhance your career. Check out Simplilearn's Full Stack (MERN Stack) Developer Master's Program in collaboration with IBM. This live, online, and interactive course will teach you the in-demand skills and prepare you for real-world scenarios.

FAQs

1. What is the difference between .NET Framework and .NET Core?

The .NET framework serves only Windows, while .NET Core supports multiple systems. Similarly, the latter lacks a few functionalities in the .NET framework.

2. Which language is best for .NET development?

C# is the top choice of language owing to its general purpose language, wide usage and great support system.

3. What should I know about .NET for a full-stack developer role?

Focus on the .NET framework and familiarity with front-end technologies and back-end development are essential to fulfilling the role's responsibilities.