Top .NET Interview Questions & Concepts Explained

Questions

1. Difference between .NET Framework, .NET Core & .NET 6/7

• Cross-platform?

• Performance?

• Microservices support?

• Hosting?

2. What is CLR, CTS, CLS?

• CLR = Runtime (memory mgmt, GC, JIT)

• CTS = Common type system

• CLS = Language interoperability rules

3. Value Type vs Reference Type

Value Type	Reference Type
Stack memory	Heap memory
Copied by value	Copied by reference

4. Boxing & Unboxing

• Convert value → object = Boxing

• Convert object → value = Unboxing

5. Garbage Collection & Generations

• Gen 0, Gen 1, Gen 2

• Managed heap

• IDisposable, using

6. Sealed, Static, Abstract Class vs Interface

Feature	Abstract	Interface
Can have implementation	Yes	.NET 8 also supports default
Multiple inherit	No	Yes

7. Async / Await & Task vs Thread

• Task uses thread pool

• Async frees thread, better scaling

8. LINQ

Examples

• Select, Where, Join, GroupBy, Any, FirstOrDefault

9. Delegates, Events, Func, Action

• Delegate = method pointer

• Event = pub-sub model

• Func<in,out> has return type

• Action<> return void

ASP.NET MVC / .NET Core

1. MVC Lifecycle

• Request → Routing → Controller → Action → View

2. Filters

• Authorization, Action, Result, Exception

3. Dependency Injection

• Constructor injection preferred

• Built-in DI container in .NET Core

4. Middleware pipeline

Use → Run → Map

5. ViewBag vs ViewData vs TempData

Feature	ViewBag	ViewData	TempData
Type	Dynamic	Dictionary	Dictionary
Life	Current request	Current req	Next request (Redirect)

6. REST API Concepts

• GET/POST/PUT/DELETE

• Status codes (200,400,401,404,500)

• CORS

• JWT auth

Entity Framework Core

1. Code-First vs Database-First

• Migrations in code-first

• Reverse engineer DB-first

2. Lazy vs Eager Loading

• Include() for eager loading

3. LINQ Joins

• join keyword or navigation properties

SQL & DB Design

1. Normalization

• 1NF, 2NF, 3NF

2. Index Types

• Clustered vs Non-clustered

• Index usage problem = slow INSERT/UPDATE

3. Stored Procedure vs Function

• Function can’t call SP

• Function must return value

4. Joins

• Inner/Left/Right/Cross

Real-Time Architecture & Security

1. SOLID Principles

• Single Responsibility, Open-Closed, etc.

2. Repository Pattern

• Abstraction over data layer

3. OAuth / JWT

• Token-based security

4. Microservices Basics

• API Gateway, Service registry, Docker

Common Coding Questions

Topic	Example
String reverse	Without Reverse()
Second highest number	LINQ
Palindrome	String & number
Remove duplicates	HashSet / LINQ
Prime number	Efficient loop logic