Tell me about yourself

Start with your current role and the parts of your experience that match the job requirements, and keep the narrative focused on the last five to ten years. For example, say, "I'm a C# developer at X, where I led a migration to .NET Core and reduced response times by 30 percent," then briefly mention a prior relevant role and why this position fits your goals. Practice a two minute version and avoid reciting your resume line by line, and do not go back to unrelated early career details.

Explain the difference between value types and reference types in C#

Describe value types as stored directly with their data, typically on the stack, and reference types as storing a reference to the data on the heap. Give a concrete example: int and struct are value types, class and string are reference types, and explain that assignment copies the value for value types and copies the reference for reference types. Mention pitfalls like boxing and unboxing, and watch out for unintended copies with large structs that can hurt performance.

What is garbage collection in .NET and how does it work

Explain that garbage collection automates memory reclamation by finding objects no longer reachable and freeing their memory, and that .NET uses generational collection to optimize for short-lived objects. Provide a brief example of generations 0, 1, and 2 and explain that frequent allocations that survive promotions end up in higher generations leading to less frequent collections. Advice: prefer implementing IDisposable for unmanaged resources and use using blocks, and avoid relying on finalizers for timely cleanup.

How do async and await work in C# and when should you use them

State that async marks a method as asynchronous and await pauses execution until a Task completes without blocking the thread, enabling responsive applications. Show a short example: public async Task GetAsync() { var result = await httpClient.GetStringAsync(url); return result; } to illustrate returning Task and awaiting asynchronous I/O. Tip: avoid blocking on async results with .Result or .Wait since that can cause deadlocks, and prefer ConfigureAwait(false) in library code when synchronization context does not matter.

What are delegates and events in C# and how do you use them

Explain that a delegate is a type-safe function pointer and an event exposes a delegate for subscribers while encapsulating invocation. Offer a small example: declare public delegate void Notify(string msg); public event Notify OnNotify; then show subscribing with OnNotify += Handler and invoking with OnNotify?.Invoke("hi"). Note common issues like null checks before invocation and that events are multicast by default, so order and exception handling inside handlers matter.

Describe the SOLID principles and how they apply to C# code

Briefly define each principle: Single Responsibility, Open/Closed, Liskov Substitution, Interface Segregation, and Dependency Inversion, and explain they guide maintainable object-oriented design. Give concise examples: keep a class focused on one responsibility, extend behavior via new classes rather than modifying existing ones, ensure derived classes can substitute base classes, create small focused interfaces, and depend on abstractions rather than concrete types. Practical tip: apply these principles incrementally, refactor when adding features, and avoid over-engineering interfaces for unlikely future needs.

How do you manage dependency injection in .NET applications

Explain that dependency injection means providing a class its dependencies from the outside, most commonly via constructor injection in .NET Core using the built-in IServiceCollection. Give an example: services.AddScoped (); then in a controller accept IRepo in the constructor and the framework resolves it at runtime. Mention service lifetimes and avoid injecting IServiceProvider as a service locator; pick the right lifetime for the dependency and be careful with scoped services in singletons.

What is LINQ and can you give an example of when to use it

Define LINQ as a set of operators for querying collections in a declarative way, supporting both query expression and method syntax for readability and composability. Show a brief example: var top = items.Where(i => i.Score > 80).OrderByDescending(i => i.Score).Take(5); which filters, sorts, and projects results in a single expression. Warn about deferred execution and the difference between IEnumerable and IQueryable, and materialize results with ToList when you need to avoid multiple enumerations.

Explain the difference between Task and Thread and when to use each

Clarify that a Thread is an OS-level execution context you manage directly, while Task represents an asynchronous operation that may run on the thread pool and is the preferred abstraction for concurrent work in modern .NET. Provide a use case: use Task.Run for CPU-bound work you want off the UI thread and use asynchronous I/O with Task-returning methods for scalable I/O-bound operations instead of creating raw threads. Be aware of thread pool limits and avoid long-running blocking operations on thread pool threads; for long-running dedicated work consider TaskCreationOptions.LongRunning or a dedicated thread.

How do you approach exception handling and logging in a C# application

State that you should catch exceptions at boundaries, log meaningful context, and rethrow or wrap exceptions when appropriate to preserve stack traces. Give an example: catch specific exceptions, log with structured properties such as userId and requestId, and avoid catching Exception unless you plan to log and rethrow or handle a truly unexpected condition. Tip: centralize logging and error handling with middleware in web apps, avoid swallowing exceptions silently, and use correlation ids to trace issues across services.

Tell me about a time you fixed a critical production bug under pressure

Situation and Task: In one role, a newly deployed release caused intermittent API failures affecting key customers, and I was asked to diagnose and fix it during business hours quickly. The goal was to restore service with minimal customer impact while identifying the root cause. Action: I reproduced the issue in a staging environment using production logs and traces, added targeted logging to capture request payloads, and rolled back the offending change while preparing a hotfix. I coordinated with QA and support to validate the fix and deployed during a low-traffic window. Result: The rollback and hotfix restored service within two hours, customer-reported incidents dropped to zero, and root cause documentation plus a pre-deployment checklist prevented recurrence.

Describe a time you disagreed with a teammate about an architecture decision

Situation and Task: During a microservices migration, a teammate recommended replicating a shared data model across services, which I believed would cause tight coupling and version drift. The task was to choose an approach that balanced independence with data consistency needs. Action: I gathered examples and trade-offs, proposed a domain-driven design approach with well-defined contracts and an anti-corruption layer, and ran a short spike to demonstrate the pattern. I presented findings in a design review and invited feedback to build consensus. Result: The team adopted the contract-based approach for new services, which reduced coupling and simplified future changes, and the spike showed lower integration effort across two pilot services.

Give an example when you had to learn a new technology quickly to deliver a project

Situation and Task: I joined a project that required moving parts of the system to Docker containers, and I had limited container experience while delivery timelines were tight. I needed to become productive fast to containerize services and update CI pipelines. Action: I followed a focused plan: read official docs, completed a short tutorial, and containerized a noncritical service as a hands-on spike to validate build and runtime behavior. I then documented the steps and patterns for the team and updated CI jobs to build and push images automatically. Result: The containerization work met the deadline, reduced environment inconsistencies for developers, and my documentation shortened onboarding time for the next two engineers joining the project.

c# developer Interview Questions: Complete Guide

Preparing for c# developer interview questions often means facing a mix of behavioral and technical problems, including coding, design, and debugging tasks. You can expect whiteboard or live coding, system design discussion, and behavioral questions, and this guide will help you structure clear, practiceable answers.

Common Interview Questions

Behavioral Questions (STAR Method)

STAR Method: Structure your answers using Situation, Task, Action, and Result to tell compelling stories about your experience.

Questions to Ask the Interviewer

Show your interest by asking thoughtful questions

•What does success look like in this role after six months, and how is it measured?
•Can you describe the current codebase architecture and any known technical debt the team is prioritizing?
•How does the team handle code reviews, testing, and deployment pipelines in daily work?
•What are the biggest engineering challenges the team expects to face in the next year?
•How do product and engineering collaborate on prioritization, and how often do you iterate on requirements?

Interview Preparation Tips

Practice coding problems with time limits and explain your thinking out loud during mock interviews to improve communication and clarity.

Read the job description closely and map your examples to required skills, preparing one strong story for each major requirement.

When writing code during an interview, state your assumptions, write clean code with small helper methods, and add quick tests or sample inputs if time allows.

Prepare three concise accomplishments with metrics, and be ready to walk through the trade-offs and decisions you made for each one.

Overview

This guide prepares you for C# developer interviews at entry, mid, and senior levels. Expect a mix of question types: 4–8 live coding problems (30–60 minutes each for whiteboard or pair sessions), 1–3 system-design problems (30–90 minutes), and behavioral rounds (30–45 minutes).

Companies often weight outcomes: correctness ~60%, code quality/readability ~25%, and communication/problem-solving ~15% in final scores.

Topics commonly tested include core C# syntax, object-oriented design, generics, LINQ, async/await, memory management and garbage collection, . NET Core/ASP.

NET, Entity Framework, unit testing, multithreading, and cloud integration (often Azure). For example, a mid-level role might include a LINQ query to transform a 10k-item list with O(n) expectations, plus an async file-processing task that must avoid deadlocks when awaiting Task.

Result.

Interviewers look beyond right answers. They evaluate how you reason about trade-offs, measure performance (e.

g. , reduce DB calls from 100 to 3 to fix an N+1 issue), and communicate changes.

For senior roles, expect architecture questions: design a notification service to handle 10,000 messages per second, explain scaling and data partitioning.

Actionable takeaway: practice 30–40 focused coding problems, create 2 small projects (API + data layer), and prepare 5 concise stories that show impact with numbers (reduced latency by X%, cut costs by Y%).

Key Subtopics & Sample Questions

Break interview prep into concrete subtopics and match each to sample questions and evaluation goals.

•Core C# and OOP
•Sample: "Implement a thread-safe singleton."
•What they assess: encapsulation, inheritance, SOLID principles, memory cost. Expect 1–2 questions.

•Generics and Type Safety
•Sample: "Explain covariance and contravariance with IEnumerable<T> vs IList<T>."
•What they assess: API design, runtime safety, examples with List<T> vs IEnumerable<T>.

•LINQ and Collections
•Sample: "Write a LINQ expression to group 100k records by userId and compute totals efficiently."
•What they assess: performance (O(n)), deferred execution, and when to use ToList().

•Async/Await and Concurrency
•Sample: "Fix deadlocks when calling async methods from sync code."
•What they assess: SynchronizationContext, ConfigureAwait(false), Task.Run trade-offs.

•Data Access / EF Core
•Sample: "Identify and fix an N+1 query that caused 100 DB calls; reduce to 3."
•What they assess: eager loading, projection, query optimization.

•Testing & CI
•Sample: "Write unit tests for a repository method using Moq and xUnit."
•Target: 70–90% coverage for core logic.

•System Design & Cloud
•Sample: "Design a scalable webhook delivery system for 10k req/sec."
•What they assess: partitioning, retries, idempotency, Azure Service Bus or Kafka.

Actionable takeaway: build a checklist covering these subtopics and practice one focused task per week for 8 weeks.

Study Resources and Practice Plan

Use targeted resources and a time-bound plan to prepare efficiently.

Books & Official Docs

•"C# in Depth" (Jon Skeet) — deep C# language features; read 2 chapters/week.
•Microsoft C# Guide and .NET docs — reference for API and runtime behavior; bookmark key pages (async, GC, Span<T>).

Courses & Tutorials

•Pluralsight: C# Path (30–60 hours total). Aim to finish core modules in 4 weeks.
•Udemy: ASP.NET Core API courses (20–30 hours) for hands-on web and EF Core examples.

Practice Platforms

•LeetCode / HackerRank: Solve 50 problems in C# across arrays, strings, trees; target 5 problems/week.
•System design: practice 8 scenario-based designs; timebox each to 45 minutes and include deployment diagrams.

Sample Projects & Repos

•eShopOnWeb (Microsoft) — study architecture and EF Core patterns; clone and run end-to-end.
•awesome-dotnet on GitHub — find real libraries and integrate one into a small project.

Mock Interviews & Metrics

•Schedule 6 mock interviews (2 with peers, 4 with paid platforms). Track metrics: average solve time, passing rate, and communication score.

8-week plan takeaway: commit 6–8 hours/week, solve 50 problems, build 2 projects, and complete 6 mock interviews to measure readiness.

c# developer Interview Questions: Complete Guide

Emily Thompson

Common Interview Questions

Behavioral Questions (STAR Method)

Questions to Ask the Interviewer

Interview Preparation Tips

Overview

Key Subtopics & Sample Questions

Study Resources and Practice Plan

Interview Prep Checklist

Build your job search toolkit

c# developer Interview Questions: Complete Guide

Emily Thompson

Common Interview Questions

Q1Tell me about yourself

Q2Explain the difference between value types and reference types in C#

Q3What is garbage collection in .NET and how does it work

Q4How do async and await work in C# and when should you use them

Q5What are delegates and events in C# and how do you use them

Q6Describe the SOLID principles and how they apply to C# code

Q7How do you manage dependency injection in .NET applications

Q8What is LINQ and can you give an example of when to use it

Q9Explain the difference between Task and Thread and when to use each

Q10How do you approach exception handling and logging in a C# application

Behavioral Questions (STAR Method)

B1Tell me about a time you fixed a critical production bug under pressure

B2Describe a time you disagreed with a teammate about an architecture decision

B3Give an example when you had to learn a new technology quickly to deliver a project

Questions to Ask the Interviewer

Interview Preparation Tips

Overview

Key Subtopics & Sample Questions

Study Resources and Practice Plan

Interview Prep Checklist

Build your job search toolkit