C# powers a huge share of enterprise and Microsoft-stack development, and its interviews test strong OOP plus .NET-specific features: value vs reference types, delegates and events, LINQ, and the async/await model. Here are the C# interview questions that actually get asked, with answers.
OOP & types
- The four OOP pillars in C# (our OOPs guide).
- Value types vs reference types — struct vs class.
- Abstract class vs interface (and what changed with default interface methods).
- Boxing and unboxing.
==vs.Equals(); ref vs out parameters.
Delegates, events & LINQ
- What is a delegate? Func, Action, and Predicate.
- Events and the observer pattern.
- Lambda expressions and LINQ — deferred vs immediate execution.
- IEnumerable vs IQueryable.
Async & memory
- async/await — how it works and common pitfalls.
- Task vs Thread; what does await actually do?
- Garbage collection and the IDisposable / using pattern.
- Managed vs unmanaged code.
How to prepare
C# rounds probe behavior and the "why". Practise explaining types, async, and LINQ out loud. Greenroom runs spoken technical interviews that follow up on your reasoning. Pair it with our OOPs and backend guides.
Frequently asked questions
What are the most common C# interview questions?
Common C# questions cover OOP, value vs reference types (struct vs class), abstract class vs interface, boxing/unboxing, == vs Equals, delegates (Func, Action, Predicate) and events, lambda expressions and LINQ (deferred vs immediate execution, IEnumerable vs IQueryable), async/await, Task vs Thread, garbage collection and the IDisposable pattern.
What is the difference between value and reference types in C#?
Value types (like int, struct and enum) store their data directly and are typically allocated on the stack, with copies being independent. Reference types (like class, string and arrays) store a reference to data on the heap, so copying the variable copies the reference and both point to the same object. This affects assignment, equality and how changes propagate.
How does async/await work in C#?
async marks a method that can contain await expressions, and await suspends the method until an awaited Task completes, returning control to the caller without blocking the thread. The compiler builds a state machine that resumes the method when the task finishes. It's ideal for I/O-bound work; common pitfalls include blocking with .Result and forgetting ConfigureAwait in libraries.
How should I prepare for a C# interview?
Focus on .NET specifics — value vs reference semantics, delegates and events, deferred LINQ execution, and how async/await really works — not just generic OOP, since those distinguish strong candidates. Practise explaining behavior out loud with a voice-based mock interview that follows up, because C# rounds probe the 'why' behind the language model.