A Bunch of C# and .NET Interview Questions and Answers

If you are interviewing for a C# and .NET developer role, you may encounter a variety of questions that cover the basics of the language, object-oriented programming, asynchronous programming, exception handling, LINQ, web development, testing, design patterns, architectures, SQL, O/RM, Agile Scrum, and more. In this article, we will explore some of the top C# and .NET interview questions, along with their answers.

Basics

1. What is C#? C# is an object-oriented programming language developed by Microsoft. It is widely used to build Windows applications, web applications, and games.

2. What is .NET? .NET is a free, open-source platform developed by Microsoft that allows developers to build applications for Windows, web, and mobile devices using different programming languages, including C#.

3. What are the features of C#? C# has several features, including garbage collection, type safety, strong typing, component-oriented programming, automatic memory management, and exception handling.

4. What is the difference between value types and reference types in C#? In C#, value types store their value directly in memory, while reference types store a reference to the memory location where the value is stored. Examples of value types include int, float, and char, while reference types include class, interface, and delegate.

5. What is boxing and unboxing in C#? Boxing is the process of converting a value type to a reference type, while unboxing is the process of converting a reference type to a value type. For example, int i = 10; object o = i; is boxing, and int j = (int)o; is unboxing.

Object-Oriented Programming

1. What is inheritance in C#? Inheritance is the process of creating a new class that derives properties and methods from an existing class. The new class is called the derived class or subclass, and the existing class is called the base class or superclass.

2. What is polymorphism in C#? Polymorphism is the ability of an object to take on many forms. In C#, polymorphism can be achieved through method overloading and method overriding.

3. What is encapsulation in C#? Encapsulation is the process of hiding the implementation details of a class and exposing only the necessary methods and properties to the outside world. This helps in maintaining the integrity of the code and prevents unwanted access to the internal workings of the class.

4. What is abstraction in C#? Abstraction is the process of creating a model that represents the important characteristics of a real-world object. In C#, abstraction can be achieved through abstract classes and interfaces.

5. What is a delegate in C#? A delegate is a type that represents a reference to a method. It is often used to implement event handling, asynchronous programming, and other tasks that require callbacks.

Asynchronous Programming

1. What is asynchronous programming in C#? Asynchronous programming is a technique in C# that allows the execution of code to continue while waiting for a long-running task to complete. This improves the performance and responsiveness of the application.

2. What is the difference between synchronous and asynchronous programming? In synchronous programming, the execution of code blocks until a task is completed, while in asynchronous programming, the execution of code continues while a task is being processed.

3. What are the advantages of using asynchronous programming? Asynchronous programming can improve the performance and responsiveness of the application, as well as provide better scalability, resource utilization, and fault tolerance.

4. How can you implement asynchronous programming in C#? Asynchronous programming can be implemented in C# through async and await keywords, Task and Task<T> classes, Parallel class, and delegates.

Exception Handling

1. What is exception handling in C#? Exception handling is the process of dealing with runtime errors that occur in a program. In C#, exceptions are objects that contain information about the error, including its type, message, and stack trace.

2. What is the purpose of try-catch blocks in C#? Try-catch blocks are used to catch and handle exceptions that occur during the execution of a program. The code that might throw an exception is placed in the try block, and the code that handles the exception is placed in the catch block.

3. What is the purpose of finally block in C#? The finally block is used to execute code that should be run regardless of whether an exception is thrown or not. This code is often used to release resources or perform clean-up operations.

4. What are some common exceptions in C#? Some common exceptions in C# include ArgumentException, ArgumentNullException, NullReferenceException, DivideByZeroException, IndexOutOfRangeException, and FileNotFoundException.

LINQ

1. What is LINQ in C#? LINQ stands for Language Integrated Query, and it is a set of features in C# that allows developers to query data from different sources using a uniform syntax.

2. What are the benefits of using LINQ? Using LINQ can simplify the code, improve the readability, and reduce the errors. It also allows developers to write more expressive queries and manipulate data easily.

3. What are the different types of LINQ queries in C#? There are three types of LINQ queries in C#: query syntax, method syntax, and mixed syntax. Query syntax uses SQL-like syntax, while method syntax uses extension methods. Mixed syntax is a combination of query and method syntax.

4. What are the standard query operators in LINQ? The standard query operators in LINQ include Where, Select, SelectMany, GroupBy, OrderBy, Join, and GroupJoin.

5. How do you join two collections using LINQ? Two collections can be joined using the Join operator in LINQ. The Join operator takes two collections, a join key, and a projection function as arguments and returns a new collection that contains elements from both collections.

Web Development

1. What is ASP.NET in C#? ASP.NET is a framework for building web applications using C#. It provides a set of tools and libraries for developing web applications, including web forms, MVC, and Web API.

2. What is the difference between web forms and MVC in ASP.NET? Web forms is a traditional approach to web development that uses server controls and postbacks, while MVC is a more modern approach that separates the application into three components: model, view, and controller.

3. What is Web API in ASP.NET? Web API is a framework for building RESTful services using C#. It allows developers to build HTTP-based services that can be accessed from different devices and platforms.

4. How do you handle authentication and authorization in ASP.NET? Authentication and authorization can be handled in ASP.NET using different techniques, including forms authentication, Windows authentication, and OAuth. Forms authentication is the most common approach, which uses cookies to store user credentials.

5. What are some popular front-end frameworks used in ASP.NET web development? Some popular front-end frameworks used in ASP.NET web development include Angular, React, and Vue.js. These frameworks are used to build interactive and dynamic user interfaces for web applications.

Testing

1. What is unit testing in C#? Unit testing is a software testing technique where individual units or components of a software application are tested in isolation. In C#, unit tests can be written using a framework like NUnit or MSTest.

2. What is test-driven development (TDD) in C#? Test-driven development is a software development approach where tests are written before the actual code. In C#, TDD can be used to improve the quality of the code and reduce the number of bugs.

3. What is mocking in C#? Mocking is a technique used in unit testing to create fake objects that mimic the behavior of real objects. In C#, mocking can be done using a mocking framework like Moq or RhinoMocks.

4. What is code coverage in C#? Code coverage is a measure of how much of the source code is executed during testing. In C#, code coverage can be measured using a tool like Visual Studio's code coverage feature.

5. What are some common testing frameworks used in C#? Some common testing frameworks used in C# include NUnit, MSTest, xUnit, and SpecFlow.

Design Patterns and Architectures

1. What are design patterns in C#? Design patterns are reusable solutions to common software design problems. In C#, design patterns can be used to solve problems related to object creation, behavior, and communication.

2. What is the Singleton pattern in C#? The Singleton pattern is a design pattern that restricts the instantiation of a class to a single object. In C#, the Singleton pattern can be implemented using a static field or a Lazy<T> type.

3. What is the Model-View-Controller (MVC) architecture in C#? The Model-View-Controller architecture is an architectural pattern that separates the application into three components: model, view, and controller. In C#, MVC can be used to develop web applications using the ASP.NET MVC framework.

4. What is the Repository pattern in C#? The Repository pattern is a design pattern that separates the data access logic from the business logic in an application. In C#, the Repository pattern can be used to access data from a database or any other data source.

5. What is dependency injection in C#? Dependency injection is a technique used to achieve loose coupling between classes in an application. In C#, dependency injection can be done using a framework like Autofac or Ninject.

SQL and O/RM

1. What is SQL in C#? SQL stands for Structured Query Language, and it is a language used to manage and manipulate relational databases. In C#, SQL can be used to interact with databases using ADO.NET.

2. What is an Object-Relational Mapping (O/RM) framework in C#? An O/RM framework is a tool that allows developers to map objects to relational databases. In C#, O/RM frameworks like Entity Framework and NHibernate can be used to perform database operations using object-oriented code.

3. What is LINQ to SQL in C#? LINQ to SQL is a component of the LINQ framework that allows developers to use LINQ queries to interact with SQL databases. In C#, LINQ to SQL can be used to write queries that are translated into SQL statements at runtime.

4. What is Entity Framework in C#? Entity Framework is an O/RM framework that allows developers to work with relational databases using object-oriented code. In C#, Entity Framework can be used to perform database operations, including querying, inserting, updating, and deleting records.

5. What is the difference between Code First and Database First approaches in Entity Framework in C#?

   The Code First approach in Entity Framework allows developers to create a database by defining the entities and their relationships in code, without having to create the database schema first. The database schema is generated automatically based on the code.

   The Database First approach, on the other hand, allows developers to create a database schema first and then generate the code that corresponds to the database schema. This approach involves creating an Entity Data Model (EDM) from an existing database schema.

Agile Scrum

1. What is Agile Scrum methodology? Agile Scrum is a methodology for managing software development projects that emphasizes collaboration, flexibility, and customer satisfaction. In Scrum, a project is divided into short sprints, each of which delivers a potentially shippable product increment.

2. What is a Scrum team in Agile Scrum? A Scrum team in Agile Scrum consists of a product owner, a Scrum master, and a development team. The product owner is responsible for defining the product backlog, the Scrum master is responsible for ensuring that the team follows Scrum practices, and the development team is responsible for delivering the product increment.

3. What is a Sprint Review in Agile Scrum? A Sprint Review is a meeting that takes place at the end of each sprint in Agile Scrum, where the team presents the product increment to the stakeholders and gathers feedback. The Sprint Review is an opportunity for the team to receive feedback on their work and make any necessary adjustments.

4. What is a Sprint Retrospective in Agile Scrum? A Sprint Retrospective is a meeting that takes place at the end of each sprint in Agile Scrum, where the team reflects on their performance and identifies ways to improve. The Sprint Retrospective is an opportunity for the team to discuss what went well, what didn't go well, and what they can do to improve in the next sprint.

5. What is a product backlog in Agile Scrum? A product backlog is a prioritized list of features, enhancements, and bug fixes that need to be developed for a product. The product backlog is owned by the product owner, and it is used to guide the team's work in each sprint.