Question 1

What is the basic difference between Value Types and Reference Types in C#, and how are they stored in memory?

Accepted Answer

Value Types inherit from System.ValueType and store their values directly (usually on the Stack or inside their containing object), while Reference Types inherit from System.Object and store references on the Stack that point to data in the Managed Heap.

Question 2

What are Boxing and Unboxing in C#, and why should they be avoided in high-volume code paths?

Accepted Answer

Boxing converts a Value Type into an object on the Heap with additional memory allocation, while Unboxing extracts the original value; repeated use burdens the Garbage Collector and slows performance.

Question 3

How do Record and Class differ in modern C#, and when should you prefer Records?

Accepted Answer

Records are designed for immutable value objects (Immutability), provide automatic value-based equality, and support non-destructive copying with the with expression.

Question 4

How do Nullable Reference Types work in C#, and what is the role of Static Flow Analysis?

Accepted Answer

They distinguish references that allow null (such as string?) from those that do not (string); the compiler uses static analysis to warn before a NullReferenceException occurs at runtime.

Question 5

How have Pattern Matching and switch expressions developed in modern C#?

Accepted Answer

They now support Property Patterns, Positional Patterns, Relational Patterns, and List Patterns for expressing complex conditions clearly and safely.

Question 6

How do Delegate, Action, and Func differ, and how does the event keyword protect encapsulation?

Accepted Answer

A Delegate is a type-safe function pointer; Func returns a value and Action returns nothing. The event keyword prevents external subscribers from invoking the event or clearing its listener list; they can only use += and -=.

Question 7

What are Span and ReadOnlySpan, and how do they process data without Heap allocation (Zero-Allocation)?

Accepted Answer

They are ref struct types that represent a contiguous window over memory (Stack, Heap, or Unmanaged Memory) and allow slicing and processing without copying data or allocating new arrays.

Question 8

How do you implement the IDisposable Pattern, and how do Managed and Unmanaged resources differ?

Accepted Answer

The CLR manages Managed resources automatically, while Unmanaged resources (such as operating system file handles and network sockets) require explicit release through IDisposable and Dispose().

Question 9

What is Variance in C#, and how do Covariance (out) and Contravariance (in) differ?

Accepted Answer

Covariance (out) allows a more specific type to be used as an output (Assignment to base), while Contravariance (in) allows a more general type to be used as an input.

Question 10

What are C# Source Generators, and how do they improve on runtime Reflection?

Accepted Answer

They are a Roslyn compiler feature that inspects code and generates real C# files during compilation, providing high performance and compile-time type checks without Reflection overhead.

C# Fundamentals & Modern Language Features Interview Questions (.NET)