Top 55+ C# Interview Questions and Answers 2026

C# Interview Questions for Freshers

Now, let us take a look at the top C# interview questions that freshers might face in an interview.

1. What is C#?

C# is a modern, object-oriented programming language developed by Microsoft. It runs on the .NET platform and is used to build web applications, desktop software, mobile apps, cloud services, games, and enterprise applications.

2. What is the difference between static, public, and void?

Public declared variables can be accessed from anywhere in the application. Static variables can be accessed globally without creating an instance of the class. Void is a type modifier that states the method and is used to specify the return type of a method in C#.

3. What is serialization?

Serialization in C# is the process of converting an object into a format that can be stored or transferred, such as a byte stream, JSON, or XML. It is commonly used when saving object data to a file, sending data over a network, or passing data between applications. The reverse process, where the stored or transferred data is converted back into an object, is called deserialization.

4. Differentiate between Break and Continue Statements

Continue statement - Used in jumping over a particular iteration and getting into the next iteration of the loop.

Break statement - Used to skip the next statements of the current iteration and come out of the loop.

5. Explain the four steps involved in the C# code compilation.

Four steps of code compilation in C# include -

• Source code compilation in managed code.
• Newly created code is clubbed with assembly code.
• The Common Language Runtime (CLR) is loaded.
• Assembly execution is done through CLR.

6. Mention the features of C# briefly.

C# is a modern, object-oriented programming language used with the .NET platform. Its key features include:

• Strong typing and type safety
• Object-oriented programming support
• Automatic memory management
• Cross-platform support with .NET
• Rich library support
• Exception handling
• Support for modern features like LINQ and async/await

These features make C# useful for building web, desktop, mobile, cloud, and enterprise applications.

Did You Know? C# ranks as the 5th most popular programming language globally with a TIOBE rating of 4.85%, placing it ahead of PHP, TypeScript, and Swift in worldwide developer adoption. (Source: TIOBE, TIOBE Programming Community Index)

7. What is a Console application?

A console application in C# is a program that runs in a command-line window instead of a graphical user interface. It takes input through the keyboard and displays output as text. Console applications are commonly used for learning C#, testing logic, building small tools, running scripts, and creating background utilities.

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OOP and C# Fundamentals Questions

These C# interview questions typically open most rounds by assessing your grasp of core OOP concepts.

8. What is an object?

An object is an instance of a class. It represents a real value created from the class blueprint and contains its own data through fields or properties. Objects are used to access the methods and members defined in a class. In C#, an object is usually created using the new keyword.

9. Define Constructors

A constructor is a member function with the same name as its class. The constructor is automatically invoked when an object is created. While the class is being initialized, it constructs all the values of data members.

10. Name all the C# access modifiers

The C# access modifiers are -

• Private Access Modifier - A private attribute or method is accessible only within the class.
• Public Access Modifier - When an attribute or method is declared public, it can be accessed from anywhere in the code.
• Internal Access Modifier - When a property or method is defined as internal, it can only be accessible from the current assembly point of that class.
• Protected Access Modifier - When a user declares a method or attribute as protected, it can only be accessed by members of that class and those who inherit it.

11. What is meant by an Abstract Class?

It's a type of class whose objects can't be instantiated, and it's signified by the term 'abstract'. It consists of a methodology or a single approach.

12. What are sealed classes in C#?

When a restriction needs to be placed on the class that needs to be inherited, sealed classes are created. In order to prevent any derivation from a class, a sealed modifier is used. A compile-time error occurs when a sealed class is forcefully specified as a base class.

13. What is method overloading?

Method overloading is the process of generating many methods in the same class with the same name but distinct signatures. The compiler uses overload resolution to determine which method to invoke at compile time.

14. What is the difference between method overriding and method overloading?

In method overriding, the relevant method definition is replaced in the derived class, thereby changing the method's behavior. When it comes to method overloading, a method is created with the same name in the same class but with different signatures.

15. What is the difference between method overriding using the override keyword and method hiding using the new keyword in C#?

The override keyword is used to extend polymorphic behavior: a virtual base method, once overridden, runs based on the object's actual type, even through a base class reference. The new keyword hides the base method, the version called depends on the reference type, and can lead to subtle bugs.

16. What is operator overloading in C#, and which operators can and cannot be overloaded?

Operator overloading enables a class to specify custom implementations of such operators as +, -, ==, and <, thereby making user-defined types behave intuitively, just as Point + Point does. Most binary, unary, and comparison operators can be overloaded in C#; assignment operators, &&, ||, and is, as, and typeof can't be.

17. How does constructor chaining work in C# using this() and base(), and why is it used?

Constructor chaining allows the use of this() in the constructor to invoke another constructor of the same class, or the base class constructor with base(). It eliminates redundant initialization code across overloads, typically by using a simple constructor that calls a detailed constructor with default arguments.

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Collections and LINQ Interview Questions

LINQ interview questions show up in almost every C# interview question round because they test trade-off reasoning.

18. What is the difference between ArrayList and Array?

An array only has items of the same type, and its size is fixed. ArrayList is similar, but it does not have a fixed size.

19. What are the differences between System.String and System.Text.StringBuilder classes?

System.String is immutable. When a string variable’s value is modified, a new memory location is assigned to the new value. The previous memory allocation gets released. System.StringBuilder, on the other hand, is designed so that it can have a mutable string in which a plethora of operations can be performed without the need for allocation of a separate memory location for the string that has been modified.

20. What are generics in C# .NET?

To reduce code redundancy, improve type safety, and enhance performance, generics can be used to create reusable classes. Collection classes can be created using generics.

21. Difference between SortedList and SortedDictionary in C#

SortedList is a collection of value pairs sorted by their keys. SortedDictionary is a collection for storing key-value pairs in sorted order, with sorting based on the key.

22. In C#, what is a Hash table class?

In C#, the Hashtable class is a collection that stores data as key-value pairs. Each key is converted into a hash code, which helps locate the value quickly.

A Hashtable is useful when you need fast lookups based on a unique key. For example, you can store employee IDs as keys and employee names as values. However, Hashtable is non-generic, so in modern C#, Dictionary<TKey, TValue> is usually preferred for its better type safety.

23. What is LINQ in C#?

LINQ, or Language Integrated Query, is a feature in C# that lets developers query data directly within the code. It can be used to retrieve and manipulate data from various sources, including arrays, collections, databases, XML, and objects.

LINQ makes data queries more readable and reduces the need for lengthy loops or complex logic. For example, it can be used to filter a list, sort records, or select specific values from a collection.

24. Compare IEnumerable<T> and IQueryable<T> in LINQ?

Use IEnumerable<T> for in-memory collections and IQueryable<T> for out-of-memory (e.g., database) queries. Queries on IEnumerable execute in memory: when you filter or sort, all data is brought into memory first. 

In contrast, IQueryable builds an expression tree that is translated (for example, into SQL) and executed by the data source. In practice, IEnumerable fetches all rows from a database into memory before filtering, whereas IQueryable adds WHERE/ORDER BY clauses, so filtering happens on the database server. Using IQueryable (as in Entity Framework) avoids transferring unnecessary data and improves performance.

25. What is the difference between List<T>, Dictionary<TKey, TValue>, and HashSet<T> in C# generic collections, and when should each be used?

• Use List<T> when order matters
• Dictionary for key lookups
• HashSet for uniqueness

26. What is deferred execution in LINQ, and how does it differ from immediate execution?

A LINQ query does not run when defined, only when enumerated, through a foreach loop or ToList(). Where() and Select() build up the query without touching the data; ToList() and Count() run it immediately. This matters because the data can change between definition and enumeration.

27. What is the difference between First(), FirstOrDefault(), Single(), and SingleOrDefault() in LINQ?

Single variants are stricter. Useful when multiple results indicate a data problem.

Delegates, Events, and Lambda Questions

This set of C# interview questions checks how delegates, lambdas, and events work under the hood.

28. What are delegates?

Delegates are essentially the same as function pointers in C++. The only difference between the two is that delegates are type-safe, while function pointers are not. Delegates are essential because they enable the creation of generic, type-safe functions.

29. What is a multicast delegate?

A multicast delegate in C# is a delegate that holds references to more than one method. When the delegate is invoked, all the methods in its invocation list are called in order.

Multicast delegates are commonly used in event handling, where a single event can trigger multiple methods. They are created using the + or += operator.

30. What are Events?

In C#, an event is a way for an object to signal another object to perform a specific action or to respond to an action or state change. Events are based on delegates and are implemented using the publisher-subscriber pattern, which is where:

• One class (the publisher) is responsible for raising events
• Other classes (subscribers) register methods to be called when the event is raised

31. What are lambda expressions in C#, and how do they relate to anonymous methods and delegates?

A lambda is a concise inline function, like x => x * 2, compiling to the same construct as an anonymous method, ultimately a delegate, a type-safe method reference. Lambdas are preferred since they're shorter and support expression trees, which anonymous methods do not.

32. What is the difference between Func<T>, Action<T>, and Predicate<T> delegate types in C#?

Predicate<T> behaves like Func<T, bool>, but reads more clearly in List<T>.Find().

33. What is the difference between the event keyword and a raw delegate field in C#?

A raw delegate field can be invoked, reassigned, or cleared by any code with access to it, risking lost subscribers. The event keyword only allows external code to use += and -=, so subscribers can register but not invoke or clear the event, making events safer to use in public APIs.

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Async/Await and Multithreading Questions

Async/await interview questions in C# usually test what's happening under the hood of the keywords.

34. What is Multithreading with .NET?

Multi-threading refers to the use of multiple threads within a single process. Each thread here performs a different function.

35. What is the Race condition in C#?

When 2 threads access the same resource and attempt to change it simultaneously, we have a race condition.

36. Why are Async and Await used in C#?

Asynchronous programming processes execute independently of the primary or other processes. Asynchronous methods in C# are created using the Async and Await keywords.

37. What is Thread Pooling in C#?

In C#, a Thread Pool is a group of threads. These threads are used to do work without interfering with the principal thread's operation.

38. How can you gracefully cancel a running Task or thread?

The recommended pattern is to use a CancellationToken. You pass a CancellationToken to your Task or async method and check token.IsCancellationRequested inside the work. This cooperative cancellation avoids forcing a thread to stop. For example, pass a CancellationToken to Task.Run and call token.ThrowIfCancellationRequested() periodically. Avoid using deprecated methods like Thread.Abort, which can corrupt the state.

39. What is the difference between Thread and Task in C# and why is Task generally preferred for async work?

A Thread is a literal OS thread that provides direct control, but it is costly to create. A Task represents an asynchronous operation that may efficiently reuse pooled threads. Task is favored because it has less overhead for cancellation and exception handling.

40. What is a deadlock in C#, and what are common strategies to prevent it in multithreaded applications?

A deadlock is a situation in which threads are waiting for each other to release resources they are holding and using. Common causes include blocking on async code with .Result or .Wait(), and locking in inconsistent order. Prevention means always waiting rather than consistently blocking and locking.

41. What does ConfigureAwait(false) do in C#, and when should it be used in async methods?

It tells the runtime not to resume on the original synchronization context after an await completes. In UI apps or older ASP.NET apps, this avoids forcing the continuation back and helps prevent deadlocks that block calls. ASP.NET Core has no such context, so the benefit is smaller there.

Advanced C# Interview Questions

These C# design patterns and memory interview questions separate candidates who write C# from those who understand it.

42. What is meant by Unmanaged or Managed Code?

In simple terms, managed code is code executed by the Common Language Runtime (CLR). This means that every application code is entirely dependent on the .NET platform and is considered under its oversight. Code executed by a runtime program that is not part of the .NET platform is considered unmanaged code. The application's runtime will handle memory, security, and other execution-related activities.

43. What is the difference between Dispose() and Finalize()methods?

Dispose() is used when an object needs to release any unmanaged resources it holds. Finalize(), on the other hand, doesn’t assure the garbage collection of an object even though it is used for the same function.

44. What are C# attributes and their significance?

C# allows developers to define declarative tags on a few entities. For instance, class and method are known as attributes. Information about the attribute can be retrieved at runtime using Reflection.

45. What is the Large Object Heap (LOH), and how is it managed?

The LOH stores large objects (≥85,000 bytes). Unlike the small object heap, the LOH is only collected during a full (gen 2) GC. Also, by default, the GC does not compact the LOH (to avoid expensive memory copying).

Instead, dead objects are swept into free lists that can be reused. .NET 4.5.1+ added GCSettings.LargeObjectHeapCompactionMode to explicitly compact the LOH on the next full GC if needed. In practice, LOH fragmentation can become problematic (e.g., unusable gaps), so for very large allocations, consider pooling or specialized data structures.

46. What is Reflection in C#, and what are its primary use cases?

Reflection allows you to examine attributes, methods, and types at runtime, even types that aren't known at compile-time. It powers serializers, DI containers, and plugins that dynamically discover members. It is slower than direct calls and is not used in critical performance paths unless cached.

47. How does the .NET garbage collector use generational collection across Gen 0, Gen 1, and Gen 2?

Garbage collector sorts objects based on their lifetimes.

• New short-lived objects are created in Gen 0 and collected more frequently.
• Survivors move to Gen 1, then Gen 2, remain there for a long time, and are infrequently collected.

48. What is the IDisposable interface, and how should the Dispose pattern be correctly implemented in C#?

The Dispose() method of IDisposable releases unmanaged resources (such as file handles) rather than waiting for garbage collection.

1. The correct pattern implements Dispose(),
2. calls GC.SuppressFinalize(this), and 
3. Exposes a protected virtual Dispose(bool) overload.

A using statement calls Dispose() automatically, even on exceptions.

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.NET Core Interview Questions

ASP.NET Core interview questions usually start with the request pipeline and dependency injection, since both shape everything else.

49. What is Kestrel, and why would you use a reverse proxy (like IIS or Nginx) with it? 

Kestrel is the high-performance, cross-platform web server for ASP.NET Core. It can serve HTTP requests directly, but in production, it’s common to put it behind a reverse proxy (e.g., IIS or Nginx). 

The proxy can handle TLS termination, host multiple sites, and provide features like process management. Kestrel alone is fast, but a reverse proxy adds robustness (and Windows Authentication if needed) while still letting Kestrel handle the application layer.

50. What is middleware in ASP.NET Core, and how is the request pipeline structured?

Middleware sits in a pipeline that each request passes through in order, where each component can inspect, modify, or short-circuit the request, then act again on the way out. The pipeline is configured in Program.cs, and the order matters because each middleware layer wraps the ones after it.

51. What is dependency injection in ASP.NET Core, and why is it important for maintainable application design?

Dependency injection lets classes receive dependencies, like services, through constructors instead of creating them directly. It decouples components, eases unit testing through mocking, and centralizes object lifetimes. C# microservices interview questions dig into DI because clean service boundaries depend on it.

52. What are the three service lifetimes in ASP.NET Core DI, Singleton, Scoped, and Transient, and how do they differ?

Injecting a scoped service into a Singleton is a common source of bugs. Entity Framework interview questions and Azure developer interview questions often build on these same DI concepts.

53. What is the generic host model in ASP.NET Core, and what role does WebApplication.CreateBuilder() play?

The generic host model is a unified startup approach in which a single host configures logging, DI, configuration, and the web server. WebApplication.CreateBuilder() sets up that host with web defaults already applied, including Kestrel, so modern programs wire up an app in a few lines.

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C# Interview Questions for Experienced Professionals

C# interview questions for 10-year-experienced developers: move toward scenario-based questions about architecture and trade-offs; no documentation answers directly.

54. What is the Observer pattern, and how does C# implement it?

The Observer pattern defines a one-to-many relationship: a subject maintains a list of observers and notifies them when its state changes. In .NET, this is commonly implemented using delegates and the event keyword.

Clients subscribe to an event (backed by a delegate) on the subject. When the subject changes, it invokes the delegate, calling all registered handlers. An event is essentially an automatic notification that some action has occurred, built on delegates. Thus, C#’s event construct encapsulates the Observer pattern.

55. What are the SOLID principles, and how do they apply to C# application architecture?

SOLID covers five principles: 

1. Single Responsibility
2. Open/Closed
3. Liskov Substitution
4. Interface Segregation
5. Dependency Inversion

In practice, this means one job per class, extending behavior rather than editing existing code, safe substitution of base classes, small interfaces, and reliance on abstractions.

56. What is the difference between layered (N-tier) architecture and clean architecture in a C# application?

Lead .NET developer interview questions often ask which fits a given system, since it depends on team size and how often the data layer changes.

57. You notice latency climbing under sustained load for a C# service handling thousands of requests per second. What performance optimization techniques would you apply?

The first step is profiling, not guessing, to confirm where the actual bottleneck sits. From there, common fixes include:

• Minimizing allocations in hot paths to ease GC pressure
• Using Span<T> and Memory<T> to avoid unnecessary copies
• Preferring structs over classes for small, short-lived data
• Caching expensive computations
• Switching blocking calls to async I/O
• Pooling connections for high-throughput endpoints

58. You are debugging a production ASP.NET Core service with gradual memory growth that leads to an OutOfMemoryException under sustained load. How would you diagnose and resolve it?

Capture memory dumps over time with dotnet-dump and compare object counts to spot what keeps growing. Common culprits include:

• Uncleared static collections
• Event handlers never unsubscribe
• Undisposed IDisposable objects

Fix the specific lifecycle issue once identified.

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