Common Interview Questions for .NET Developers (ASP.NET, C#, SQL Server)

ASP.NET

1. Explain the ASP.NET page life cycle.
   • Discuss the stages from initialization to rendering, including events like Page_Init, Page_Load, Page_PreRender, and Page_Unload.
2. What is the difference between ASP.NET Web Forms and ASP.NET MVC?
   • Highlight key differences in architecture, control, flexibility, and usage scenarios. Explain how MVC provides separation of concerns and is more suited for modern web applications.
3. How do you handle state management in ASP.NET?
   • Discuss techniques like ViewState, Session State, Application State, Cookies, and Query Strings. Explain when to use each method.
4. What are HttpHandlers and HttpModules?
   • Describe how HttpHandlers are responsible for processing incoming HTTP requests and HttpModules are used to inspect and/or modify the request and response.
5. Explain the role of Global.asax in an ASP.NET application.
   • Discuss its usage for application-level event handling, such as Application_Start, Session_Start, Application_BeginRequest, and Application_End.
6. What is Web API, and how does it differ from WCF?
   • Explain the usage of Web API for creating RESTful services and how it differs from WCF in terms of configuration, protocol support, and ease of use.
7. How do you implement authentication and authorization in ASP.NET?
   • Discuss methods like Forms Authentication, Windows Authentication, and OAuth. Explain the use of attributes like [Authorize] and role-based authorization.
8. What are Razor Pages in ASP.NET Core?
   • Describe the Razor Pages framework, its benefits over traditional MVC for simple page-focused scenarios, and how it simplifies page programming.
9. How do you handle error handling and logging in ASP.NET?
   • Discuss the use of try-catch blocks, custom error pages, the Global.asax file, and logging frameworks like NLog, Serilog, or built-in logging in ASP.NET Core.
10. What is Dependency Injection, and how is it used in ASP.NET Core?
    • Explain the concept of Dependency Injection (DI), its benefits, and how ASP.NET Core implements DI using the built-in service container.

C#

1. Explain the difference between value types and reference types in C#.
   • Describe how value types are stored on the stack and reference types on the heap. Provide examples of each.
2. What is the difference between public, private, protected, and internal access modifiers?
   • Explain the scope and visibility of each access modifier within and outside of assemblies and classes.
3. What is LINQ, and how is it used in C#?
   • Discuss Language Integrated Query (LINQ), its syntax, and how it is used to query collections, databases, XML, etc.
4. How do you implement exception handling in C#?
   • Describe the use of try-catch blocks, finally statements, and custom exception classes.
5. What is the purpose of the async and await keywords in C#?
   • Explain asynchronous programming, how async and await simplify writing asynchronous code, and provide a simple example.
6. What are delegates and events in C#?
   • Describe delegates as type-safe function pointers and how they are used to define events. Provide an example of event subscription and invocation.
7. What is the difference between an abstract class and an interface in C#?
   • Highlight key differences in usage, inheritance, and implementation. Explain scenarios where each should be used.
8. What is garbage collection, and how does it work in .NET?
   • Discuss the automatic memory management system in .NET, how garbage collection works, and concepts like generations, finalization, and disposal.
9. Explain the SOLID principles in C#.
   • Describe each of the SOLID principles (Single Responsibility, Open/Closed, Liskov Substitution, Interface Segregation, and Dependency Inversion) and how they guide object-oriented design.
10. What are generics in C#, and why are they useful?
    • Explain the concept of generics, how they promote type safety and reusability, and provide examples of generic classes and methods.

SQL Server

1. What are the different types of joins in SQL Server?
   • Describe INNER JOIN, LEFT JOIN, RIGHT JOIN, FULL OUTER JOIN, CROSS JOIN, and provide examples of their usage.
2. Explain the concept of indexing in SQL Server.
   • Discuss clustered and non-clustered indexes, their importance in query performance, and the impact on insert/update/delete operations.
3. How do you optimize a SQL query?
   • Provide strategies for query optimization, such as indexing, query refactoring, avoiding subqueries, and using execution plans.
4. What is the difference between a primary key and a unique key?
   • Explain the uniqueness constraint of both, differences in nullability, and their role in database design.
5. How do you handle transactions in SQL Server?
   • Discuss the concept of transactions, ACID properties, and SQL statements like BEGIN TRANSACTION, COMMIT, and ROLLBACK.
6. What are stored procedures and functions in SQL Server?
   • Explain the difference between stored procedures and functions, their use cases, and how they improve performance and security.
7. What is normalization, and why is it important in database design?
   • Describe normalization, the different normal forms (1NF, 2NF, 3NF, etc.), and how normalization reduces redundancy and improves data integrity.
8. How do you use the GROUP BY clause in SQL Server?
   • Explain the GROUP BY clause, its syntax, and how it is used to aggregate data using functions like SUM, COUNT, AVG, etc.
9. What are triggers in SQL Server?
   • Discuss the purpose of triggers, types of triggers (DML, DDL, LOGON), and provide examples of their usage in enforcing business rules.
10. How do you implement error handling in SQL Server?
    • Explain the use of TRY…CATCH blocks, how to handle exceptions, and log errors in SQL Server.