.NET Interview Questions

Question 1

What is .NET and what is the CLR?

Accepted Answer

.NET is a cross-platform framework. CLR (Common Language Runtime) manages memory, security, and execution of .NET programs. .NET supports C#, F#, VB.NET. CLR provides: garbage collection, JIT compilation (IL to native code), type safety, exception handling, thread management. .NET Core â†’ .NET 5+ is cross-platform. NuGet is the package manager.

Question 2

What is ASP.NET Core?

Accepted Answer

ASP.NET Core is a cross-platform web framework for building APIs, web apps, and microservices with C#. Features: middleware pipeline, dependency injection (built-in), Razor Pages, MVC, Web API, Blazor (WebAssembly), SignalR (real-time). Kestrel web server. Configuration: appsettings.json, environment variables. Modern: minimal APIs (.NET 6+), native AOT compilation (.NET 8).

Question 3

What is Entity Framework Core?

Accepted Answer

EF Core is .NET's ORM mapping C# classes to database tables with LINQ queries and automatic migrations. Code-first: define C# models, generate migrations. DbContext: database session. LINQ: type-safe queries. Supports: SQL Server, PostgreSQL, SQLite, MySQL. Features: lazy/eager/explicit loading, change tracking, migrations, raw SQL. Alternatives: Dapper (micro-ORM, faster for simple queries).

Question 4

What is dependency injection in .NET?

Accepted Answer

DI is built into ASP.NET Core: register services in Program.cs, inject via constructors with Scoped/Transient/Singleton lifetimes. Lifetimes: Transient (new each time), Scoped (per request), Singleton (app lifetime). Register: builder.Services.AddScoped<IService, Service>(). Inject: constructor injection. Benefits: testability, loose coupling, configurable. AutoFac/Scrutor for advanced scenarios. Interface-based for abstraction.

Question 5

What is async/await in C#?

Accepted Answer

async/await enables non-blocking I/O operations, freeing threads to handle other requests while waiting for results. async marks method as asynchronous, await suspends until Task completes without blocking thread. Task/Task<T> represent async operations. ConfigureAwait(false) for library code. Avoid async void (except event handlers). Parallel: Task.WhenAll for concurrent operations. IAsyncEnumerable for streaming. Deadlock risk with .Result in sync context.

Question 6

Design a REST API with ASP.NET Core.

Accepted Answer

Use controllers or minimal APIs, EF Core for data, JWT authentication, middleware pipeline, and Swagger documentation. Architecture: (1) Minimal API or controllers. (2) EF Core + repository pattern. (3) DTOs with AutoMapper. (4) JWT auth with ASP.NET Identity. (5) Middleware: logging, exception handling, CORS. (6) Swagger/OpenAPI documentation. (7) Rate limiting. (8) Health checks. (9) Docker deployment.

Question 7

Microsoft: How does .NET achieve cross-platform support?

Accepted Answer

.NET compiles to IL (Intermediate Language), then JIT compiles to native code on each platform via platform-specific runtimes. .NET 5+ unified: Windows, Linux, macOS, mobile (MAUI). CoreCLR: cross-platform runtime. RyuJIT: JIT compiler. Native AOT (.NET 8): compile directly to native code, no JIT needed. Mono runtime for mobile/WebAssembly. Single codebase, multiple platforms.

Question 8

Question 9

What is the .NET Framework vs .NET Core vs .NET 5+?

Accepted Answer

.NET Framework is Windows-only legacy; .NET Core is cross-platform; .NET 5+ unified both into one cross-platform platform. .NET Framework: Windows-only, mature, WinForms/WPF/ASP.NET. .NET Core: cross-platform, open-source, high-performance rewrite. .NET 5+: unified platform combining Framework and Core â€” cross-platform, open-source. .NET 6 LTS, .NET 7, .NET 8 LTS are latest. Migration: new projects should use .NET 8+. ASP.NET Core replaces ASP.NET MVC/Web API. Entity Framework Core replaces EF6. MAUI replaces Xamarin for mobile.

Question 10

What is the difference between value types and reference types in C#?

Accepted Answer

Value types store data directly on stack (int, struct); reference types store a reference to heap-allocated data (class, string). Value types: int, double, bool, char, struct, enum â€” stored on stack, copied on assignment, no null (unless nullable int?). Reference types: class, string, array, delegate, interface â€” stored on heap, variable holds reference, can be null. Boxing: value type â†’ object (heap allocation). Unboxing: object â†’ value type. struct vs class: struct is value type (small, immutable data), class is reference type. string is immutable reference type with value-type semantics. Span<T> and stackalloc for stack-allocated arrays.

.NET Development Course

What's Inside Every Lesson?

Who This Course Is For

Prerequisites

What You'll Learn

Career Opportunities

Course Completion Certificate

Course Modules Overview

C# Fundamentals & .NET Basics

Advanced C# & OOP Concepts

ASP.NET Core Web Development

Entity Framework & Database

Web API Development

Authentication & Security

Testing & Quality Assurance

Cloud Integration & Deployment

Advanced .NET Patterns & Performance

Advanced Dotnet Patterns and Architecture

Dotnet Performance and Optimization

Dotnet Deployment and DevOps

Course Curriculum

C# Fundamentals & .NET Basics

Advanced C# & OOP Concepts

ASP.NET Core Web Development

Entity Framework & Database

Web API Development

Authentication & Security

Testing & Quality Assurance

Cloud Integration & Deployment

Advanced .NET Patterns & Performance

Advanced Dotnet Patterns and Architecture

Dotnet Performance and Optimization

Dotnet Deployment and DevOps

Your Learning Roadmap

Tools & Technologies

.NET 8

Visual Studio 2022

Entity Framework Core

Azure

Docker

xUnit

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