Infosys .NET Developer Interview Questions 2026: C#, ASP.NET Core, SQL and Azure (30 Q&A)

.NET is one of the largest lateral hiring streams at Infosys, because a big share of its banking, insurance and manufacturing clients run on Microsoft stacks. The interview is not exotic: C# fundamentals, ASP.NET Core, Entity Framework, SQL Server, some Azure, often some Angular, and a scenario or two from real delivery work. This page explains how the process runs in 2026, what interviewers actually probe, and gives 30 questions with sample answers for freshers moving into .NET and laterals with one to five years.

The pattern in candidate reports is consistent: Infosys panels ask a concept, then ask where you used it, then ask what went wrong. Prepare every answer in that shape.

How the Infosys .NET developer process works in 2026

As of September 2026, candidate reports describe two variants.

Lateral hiring (1 to 5+ years). A May 2026 interview experience published on Medium describes the process as mainly two rounds: a coding round and a technical interview, with the focus on problem-solving, .NET fundamentals, SQL, Azure basics, Angular and real-world development scenarios, at a moderate to difficult level for one to five years of experience. A GeeksforGeeks .NET developer experience reports the technical round leaning heavily on OOP concepts alongside database and coding questions. HR follows, covering notice period, CTC expectations and location. Some accounts add a managerial round or a client interview before the offer.

Freshers. Campus and off-campus freshers come through Infosys's online assessment (aptitude, reasoning, verbal and pseudocode), then a technical interview and HR. Allocation to a .NET stream happens during or after training, so the fresher interview is broader; the C# and SQL groups below are the ones to prioritise.

Duration. Forty-five to sixty minutes for the main technical round, twenty to thirty for a screen, fifteen for HR.

Difficulty. Glassdoor's aggregate for Infosys Dot NET Developer interviews shows 3.3 out of 5 for difficulty, with 47 percent of respondents rating the experience positive.

Compensation. Infosys does not publish role-wise CTC on its careers site, and forum figures vary widely by band and location. Ask the recruiter for the band and get fixed, variable and joining bonus in writing.

What the Infosys .NET interviewer is testing

• C# depth for your years. OOP with examples for freshers; generics, async, memory and LINQ internals for laterals.
• ASP.NET Core understanding. Middleware, dependency injection, Web API design, authentication.
• Data access judgement. Entity Framework Core versus raw SQL, N+1 problems, transactions, indexing.
• SQL by hand. Joins, group by, window functions, stored procedures.
• Cloud and front-end awareness. Azure services you have touched; Angular basics if the project is full stack.
• Delivery sense. How you debug a production issue, review code, and handle a change request.

30 Infosys .NET developer interview questions with sample answers

C# and OOP

1. Value types versus reference types, and what is boxing?

"Value types (int, struct, enum) hold data directly and live on the stack or inline in an object; reference types (class, string, arrays) hold a reference to heap memory. Boxing converts a value type into an object, allocating on the heap; unboxing casts it back. It matters for performance in hot loops and when using non-generic collections like ArrayList. Generics exist largely to avoid it."

2. Abstract class versus interface in C#. When do you choose which?

"An abstract class can hold state, constructors and implemented members, and a class inherits only one. An interface is a contract, a class can implement many, and since C# 8 it can carry default implementations. I use an interface for a capability such as IPaymentGateway so I can mock it in tests, and an abstract class when several implementations share real code, such as a BaseRepository."

3. Explain virtual, override, new and sealed.

"virtual marks a base method as overridable; override replaces it in a derived class with runtime polymorphism. new hides the base method instead of overriding it, so the method called depends on the declared type, which is almost always a bug waiting to happen. sealed on a class prevents inheritance; on an override it prevents further overriding."

4. What is the difference between IEnumerable and IQueryable?

"IEnumerable executes in memory; once you have it, every Where runs on the client. IQueryable builds an expression tree that a provider like EF Core translates to SQL, so filtering happens in the database. The classic bug is .ToList() before .Where(), pulling a million rows to filter ten. I return IQueryable from repositories only when the caller is in the same layer; otherwise a materialised list or DTOs."

5. Explain async and await. What does ConfigureAwait(false) do?

"async methods return a Task and await yields control until the awaited task completes without blocking the thread, which is why a web server can serve other requests meanwhile. ConfigureAwait(false) tells the continuation not to capture the synchronisation context; in ASP.NET Core there is no context so it rarely matters, but in libraries it avoids deadlocks when someone calls .Result. The rule I follow: async all the way, never .Result or .Wait()."

6. How does garbage collection work, and when do you implement IDisposable?

"The GC is generational: new objects in Gen 0, survivors promoted to Gen 1 and Gen 2, collected less often. It frees managed memory automatically but knows nothing about unmanaged resources: file handles, database connections, sockets. Those need IDisposable and a using block so they release deterministically. DbContext, HttpClient created manually, and StreamReader are the ones people forget."

7. string versus StringBuilder, and why is string immutable?

"string is immutable: every concatenation allocates a new object, so a loop building a large string is O(n²) in allocations. StringBuilder mutates a buffer. Immutability makes strings thread-safe, hashable as dictionary keys and interned safely. I use StringBuilder in loops and string interpolation elsewhere."

8. What are delegates and events? Give a use from your project.

"A delegate is a type-safe reference to a method; Func and Action are the generic built-ins. An event wraps a delegate so outside code can subscribe and unsubscribe but not invoke it. In an order service I raised an OrderPlaced event that the email and inventory modules subscribed to, which kept the order code from knowing about them."

ASP.NET Core and Web API

9. Explain the ASP.NET Core middleware pipeline.

"Requests pass through middleware components in the order registered in Program.cs: exception handling, HTTPS redirection, static files, routing, authentication, authorisation, then endpoints. Each can short-circuit or call next. Order matters: authentication before authorisation, exception handler first so it wraps everything. I wrote a middleware to add a correlation ID header for log tracing."

10. What are the dependency injection lifetimes, and what goes wrong with a wrong choice?

"Transient: new instance per resolution. Scoped: one per HTTP request. Singleton: one for the app lifetime. DbContext must be scoped; registering it as singleton shares one context across requests and causes threading errors and stale data. Injecting a scoped service into a singleton is a captive dependency; the container throws in development if validation is on."

11. How do you design a RESTful Web API for orders?

"Resources as nouns: GET /api/orders, GET /api/orders/{id}, POST /api/orders, PUT /api/orders/{id}, DELETE /api/orders/{id}, with GET /api/orders/{id}/items for sub-resources. Return 201 with a Location header on create, 404 when missing, 400 with validation details, 409 on conflicts. Use DTOs, not entities, in the contract, version the API in the route or header, and paginate list endpoints."

12. How do you implement authentication and authorisation in ASP.NET Core?

"For APIs, JWT bearer: AddAuthentication().AddJwtBearer() validating issuer, audience, lifetime and signing key, then [Authorize] on controllers. Authorisation through roles or policies, [Authorize(Policy = "CanApprove")] with a requirement handler. For an enterprise client, tokens usually come from Azure AD or an identity server rather than our own login endpoint."

13. How do you handle exceptions globally?

"A single exception-handling middleware or UseExceptionHandler that logs the exception with the correlation ID and returns a ProblemDetails response. Domain exceptions map to 400 or 404; anything else to 500 with no stack trace in production. Controllers stay free of try-catch, and the log has enough context to reproduce."

14. What is model validation, and how do you validate a complex rule?

"Data annotations like [Required] and [Range] run automatically with [ApiController] and return 400. For complex rules such as 'discount cannot exceed 20 percent for new customers', I use FluentValidation or a custom IValidatableObject, and keep business rules in the service layer so they apply to non-HTTP callers too."

15. Difference between .NET Framework and .NET 8, and how did you migrate?

".NET Framework is Windows-only and in maintenance; .NET 8 is cross-platform, faster, with unified BCL and long-term support. Migration steps I have done: upgrade to .NET Standard-compatible libraries, replace Web.config with appsettings.json, replace System.Web dependencies, move from Entity Framework 6 to EF Core, and run the .NET Upgrade Assistant to find the rest."

Entity Framework Core and SQL

16. Code-first versus database-first, and how do migrations work?

"Code-first: entities and DbContext define the schema, migrations generate SQL to evolve it. Database-first: scaffold entities from an existing database, common with legacy client systems. Migrations are versioned classes with Up and Down; I review the generated SQL before applying it in production and never let the app auto-migrate on startup in a shared environment."

17. What is the N+1 problem, and how do you avoid it in EF Core?

"Loading a list of orders then accessing order.Customer in a loop fires one query per order. Fix with Include for eager loading, or project into a DTO with Select so only the needed columns come back in one query. I turn on query logging in development to catch it. Lazy loading is off by default in EF Core, which is a good thing."

18. Write a SQL query for the top three highest-paid employees in each department.

"SELECT * FROM (SELECT name, dept_id, salary, DENSE_RANK() OVER (PARTITION BY dept_id ORDER BY salary DESC) AS rnk FROM employees) t WHERE rnk <= 3; DENSE_RANK handles ties; ROW_NUMBER would drop one of two equal salaries. Without window functions, a correlated subquery counting higher salaries per department works but is slower."

19. Stored procedure versus function, and when do you use a procedure from EF Core?

"A function returns a value and can be used in a SELECT; it cannot change data. A procedure can modify data, return multiple result sets and use transactions. I call procedures from EF Core with FromSqlRaw or ExecuteSqlRaw for heavy set-based operations that would be slow as LINQ, such as a month-end batch, and keep simple CRUD in LINQ."

20. How do you find and fix a slow query?

"Look at the execution plan for scans on large tables, missing indexes and key lookups. Check for functions on indexed columns in WHERE, implicit conversions, and SELECT *. Add a covering index if the query is frequent, rewrite the predicate to be sargable, and measure again. In one project a WHERE CAST(created_at AS DATE) = @d scanned a 40-million-row table; rewriting as a range predicate made it use the index."

21. Explain transactions and isolation levels in SQL Server.

"A transaction groups statements atomically. Isolation levels trade consistency for concurrency: Read Uncommitted allows dirty reads; Read Committed, the default, prevents them; Repeatable Read prevents non-repeatable reads; Serializable prevents phantoms; Snapshot uses row versioning so readers do not block writers. In EF Core I wrap multi-table updates in BeginTransaction and keep them short."

Azure, Angular and delivery

22. Which Azure services have you used, and for what?

Name only what you have touched. "App Service for hosting the API with deployment slots for zero-downtime releases, Azure SQL as the database, Key Vault for connection strings and secrets, Application Insights for logging and performance, and a Function on a timer for a nightly report job." If you have not used Azure, say what you deployed to and how you would map it.

23. How does your Angular front end call the .NET API, and how do you handle errors?

"An Angular service wraps HttpClient calls returning observables; components subscribe, often through the async pipe. An HTTP interceptor attaches the JWT and catches errors globally, mapping 401 to a redirect to login and 500 to a toast. CORS is configured on the API for the front-end origin only."

24. How do you unit test a service that depends on a repository?

"Inject the repository as an interface, mock it with Moq in an xUnit test, arrange the mock to return known data, act by calling the service, and assert on the result and on Verify calls. Business logic stays testable without a database. For the data layer I use the EF Core in-memory provider or SQLite for a few integration tests."

25. Explain SOLID with one example each from .NET code.

"Single responsibility: a controller that only maps HTTP to a service. Open-closed: adding a new discount rule as a new IDiscountRule implementation rather than editing a switch. Liskov: any IRepository<T> mock behaves like the real one. Interface segregation: IReadRepository separate from IWriteRepository. Dependency inversion: services depend on interfaces resolved by the container, not on concrete classes."

Scenario and HR

26. Production API is returning 500 for some users after a deployment. What do you do?

"Check Application Insights for the exception and the failing request pattern. If it is a code bug affecting many users, swap the deployment slot back and fix forward. If it is data-specific, reproduce with that data in staging. Communicate status to the lead every thirty minutes, and write a short root-cause note afterwards, including the test that should have caught it."

27. A client asks for a change that will break an existing integration. How do you respond?

"Explain the impact with specifics, propose a versioned endpoint so both behaviours coexist, give an estimate for each option, and let the client and my lead decide. I would not silently break the integration and I would not refuse outright."

28. Explain your current project's architecture in three minutes.

Layers, hosting, database, integrations, your ownership, one problem you solved, and numbers where you have them: users, requests per day, data size. Practise this aloud; laterals are largely judged on it.

29. Why are you leaving, and what is your notice period?

"My current project is in support mode with little development. I want a build role on .NET 8 and Azure, which this opening is. Notice period is 90 days, negotiable to 60 with leave adjustment and buyout allowed." Have the exact policy ready.

30. What are your salary expectations?

Give a range anchored on the band: "Based on the role and my experience, I am looking at a range of X to Y, and I am open to discussing the structure." Do not quote a number before you know the band; ask the recruiter first.

Mistakes that get .NET candidates rejected at Infosys

• Concepts without usage. "A singleton is a class with one instance" fails the follow-up; "I registered the cache as a singleton and here is why" passes.
• Not knowing EF Core well enough to spot N+1 or explain migrations.
• Blocking on async with .Result and defending it.
• SELECT * and no index awareness in SQL answers.
• Zero Azure vocabulary for a 2026 .NET role.
• A vague notice period or CTC expectation in HR.

How to practise the Infosys .NET developer round

This interview is won by explaining code you have written and decisions you have made, under follow-up questions, with one live coding task in the middle. Reading concept lists does not train that; speaking answers and getting feedback does.

In MockMate Practice, attach your resume and paste the Infosys .NET job description, choose a technical round and run an adaptive session in the browser. The interviewer persona asks about your project, pushes on the C#, EF Core and SQL answers you give, and sets a coding problem you solve in the built-in editor. The report shows each answer, response timing, coaching evidence and the weaknesses that recur, with a recommended next practice. Eligible accounts get three free Practice starts of up to ten minutes each as of September 2026. Use MockMate Live assistance only in interviews or meetings where the organisation or interviewer permits it; Infosys selection rounds do not, so stay with Practice for this interview.

A one-week plan: three days of C# and SQL questions spoken aloud with a "where I used it" ending; one day rewriting your project explanation; a Practice round, a report read, and a second round on the weakest group. For the wider process see the Infosys hub, and for the manager conversation the Infosys managerial round page.