Top 70 C# / .NET Interview Questions & Answers (2026)

01 What is C#? 02 What is the .NET platform? 03 What is the difference between value types and reference types in C#? 04 What is the difference between a class and a struct in C#? 05 What are access modifiers in C#? 06 What is inheritance in C#? 07 What is polymorphism in C#? 08 What is an interface in C#? 09 What is the difference between abstract class and interface in C#? 10 What is encapsulation in C#? 11 What is a property in C# and how does it differ from a field? 12 What is a constructor in C#? 13 What is a delegate in C#? 14 What is an event in C#? 15 What is LINQ in C#? 16 What is async/await in C#? 17 What is the difference between Task and Thread in C#? 18 What is garbage collection in C#? 19 What is IDisposable and the using statement? 20 What is exception handling in C#? 21 What are generics in C#? 22 What is the difference between == and .Equals() in C#? 23 What are extension methods in C#? 24 What is a lambda expression in C#? 25 What is var in C#? 26 What is the difference between String and StringBuilder in C#? 27 What is the difference between Array and List<T> in C#? 28 What is a namespace in C#? 29 What is the static keyword in C#? 30 What is null safety in C#? 31 What is a record type in C#? 32 What is pattern matching in C#? 33 What is the difference between ref, out, and in parameters in C#? 34 What is the sealed keyword in C#? 35 What are tuples in C#? 36 What is the IEnumerable interface?

01 What is ASP.NET Core and how does it differ from ASP.NET Framework? 02 What is middleware in ASP.NET Core? 03 What is dependency injection in ASP.NET Core? 04 What is Entity Framework Core? 05 What is the difference between eager, lazy, and explicit loading in EF Core? 06 What is the Task Parallel Library (TPL) in C#? 07 What is a CancellationToken in C#? 08 What are memory-related performance features in modern C#? 09 What is reflection in C#? 10 What are attributes in C#? 11 What is the difference between IQueryable and IEnumerable in LINQ? 12 What is a ConcurrentDictionary and when should you use it? 13 What is the Observer pattern and how is it implemented in C#? 14 What is the Repository pattern in C#? 15 What is the CQRS pattern in C#? 16 What is SignalR? 17 What is middleware authentication vs authorization in ASP.NET Core? 18 What is a hosted service in ASP.NET Core? 19 What is the difference between AddSingleton, AddScoped, and AddTransient? 20 What are source generators in C#? 21 What is the ILogger interface in ASP.NET Core? 22 What is options pattern in ASP.NET Core?

01 What are expression trees in C#? 02 What is the difference between value tasks and tasks in C#? 03 What is Native AOT compilation in .NET? 04 What are channels in C# and how do they work? 05 What is the IAsyncEnumerable interface and how is it used? 06 What are covariance and contravariance in C# generics? 07 What is the Roslyn compiler API? 08 What is the actor model in C# with Akka.NET or Orleans? 09 What is GC pressure and how do you diagnose and fix it? 10 What is the difference between process and AppDomain in .NET? 11 What is System.Text.Json and how does it compare to Newtonsoft.Json? 12 How do you implement caching in ASP.NET Core?