Basic C# Interview Questions

Below are Basic C# Interview Questions:

Basic Concepts:

1. What is C#?
   • Answer: C# (pronounced C-sharp) is a modern, object-oriented programming language developed by Microsoft as part of the .NET initiative.
2. Explain the difference between == and .Equals() in C#.
   • Answer: == is used for comparing values, while .Equals() is used for comparing the content of objects.
3. What is the difference between ref and out parameters in C#?
   • Answer: ref parameters need to be initialized before they are passed to the method, while out parameters do not need to be initialized.
4. What is the var keyword used for in C#?
   • Answer: var is used for implicit typing, allowing the compiler to determine the variable’s type based on the assigned value.
5. Explain the Nullable<T> type in C#.
   • Answer: Nullable<T> allows value types to have a value of null by wrapping them in a nullable container.

Object-Oriented Programming:

6. What is polymorphism in C#?
   • Answer: Polymorphism allows objects of different types to be treated as objects of a common base type, enabling code reusability.
7. Explain the concept of inheritance in C#.
   • Answer: Inheritance allows a class (derived/child) to inherit properties and behaviors from another class (base/parent).
8. What is encapsulation in C#?
   • Answer: Encapsulation is the bundling of data and methods that operate on that data into a single unit (class).
9. What is abstraction in C#?
   • Answer: Abstraction is the process of simplifying complex systems by modeling classes based on the essential properties and behaviors.
10. What is the purpose of the base keyword in C#?
    • Answer: The base keyword is used to access members of the base class from a derived class.

C# Language Features:

11. What is the difference between readonly and const in C#?
    • Answer: readonly can be assigned at runtime, while const is a compile-time constant and must be assigned a value at declaration.
12. What is a delegate in C#?
    • Answer: A delegate is a type that represents references to methods with a specific signature, allowing for method invocation through the delegate.
13. Explain the async and await keywords in C#.
    • Answer: async defines an asynchronous method, and await is used to asynchronously wait for a task to complete.
14. What are the different access modifiers in C#?
    • Answer: public, private, protected, internal, protected internal.
15. What is the purpose of the using statement in C#?
    • Answer: The using statement is used for resource management, ensuring that IDisposable objects are properly disposed of after use.

Exception Handling:

16. What is an exception in C#?
    • Answer: An exception is a runtime error that occurs during the execution of a program, disrupting the normal flow of instructions.
17. Explain the difference between throw and throw ex in C# exceptions.
    • Answer: throw ex resets the stack trace, potentially losing information, while throw preserves the original stack trace.
18. What is the purpose of the finally block in C# exception handling?
    • Answer: The finally block is used to execute code that should always run, whether an exception is thrown or not.

Collections:

19. What is the difference between List<T> and Dictionary<K, V> in C#?
    • Answer: List<T> is an ordered collection, while Dictionary<K, V> is a key-value pair collection.
20. Explain the purpose of the IEnumerable and IEnumerator interfaces.
    • Answer: IEnumerable provides a way to iterate over a collection, and IEnumerator defines methods for iterating through the elements of a collection.

LINQ:

21. What is LINQ?
    • Answer: LINQ (Language Integrated Query) is a set of features in C# that provides a consistent query syntax to query different types of data sources.
22. Explain the difference between IEnumerable and IQueryable in LINQ.
    • Answer: IEnumerable is suitable for querying in-memory collections, while IQueryable is suitable for querying external data sources like a database.

File Handling:

23. How can you read from a file in C#?
    • Answer: Use the StreamReader class to read text from a file or BinaryReader for binary files.
24. Explain the purpose of the using statement when working with files in C#.
    • Answer: The using statement ensures proper disposal of resources, like file handles, after their usage is completed.

Threading:

25. What is the purpose of the lock statement in C#?
    • Answer: The lock statement is used to synchronize access to a shared resource in a multithreaded environment.
26. Explain the difference between Task and Thread in C#.
    • Answer: Task is a higher-level abstraction for parallelism and asynchronous programming, while Thread is a lower-level construct.

ASP.NET and Web Development:

27. What is ASP.NET?
    • Answer: ASP.NET is a web development framework for building modern, dynamic web applications.
28. What is the difference between ASP.NET Web Forms and ASP.NET MVC?
    • Answer: Web Forms follows the traditional event-driven programming model, while MVC follows the model-view-controller pattern.

Serialization:

29. What is serialization in C#?
    • Answer: Serialization is the process of converting an object into a format that can be easily persisted or transmitted, such as JSON or XML.
30. Explain the purpose of the [Serializable] attribute in C#.
    • Answer: The [Serializable] attribute indicates that a class can be serialized, allowing its instances to be converted to and from binary or XML formats.

Dependency Injection:

31. What is dependency injection in C#?
    • Answer: Dependency injection is a design pattern where the dependencies of a class are injected from the outside rather than being created within the class.

Reflection:

32. What is reflection in C#?
    • Answer: Reflection allows inspection and manipulation of metadata, types, and objects at runtime.
33. Explain the purpose of the typeof operator in C# reflection.
    • Answer: typeof is used to obtain the Type object representing a specified type at compile time.

Testing:

34. What is unit testing?
    • Answer: Unit testing is a software testing method where individual units or components of a software application are tested in isolation.

Design Patterns:

35. Explain the Singleton design pattern in C#.
    • Answer: The Singleton pattern ensures a class has only one instance and provides a global point of access to it.
36. What is the Factory Method design pattern?
    • Answer: The Factory Method pattern defines an interface for creating an object but allows subclasses to alter the type of objects that will be created.

ASP.NET Core:

37. What is ASP.NET Core?
    • Answer: ASP.NET Core is a cross-platform, high-performance, open-source framework for building modern, cloud-based, and internet-connected applications.
38. Explain the concept of middleware in ASP.NET Core.
    • Answer: Middleware in ASP.NET Core is software components that handle requests and responses as they move through the pipeline.

Entity Framework:

39. What is Entity Framework in C#?
    • Answer: Entity Framework is an Object-Relational Mapping (ORM) framework that simplifies database operations by allowing developers to work with objects.
40. Explain the Code-First approach in Entity Framework.
    • Answer: The Code-First approach involves defining the data model using C# classes, and the database schema is automatically generated based on these classes.

Security:

41. What is Cross-Site Scripting (XSS)?
    • Answer: XSS is a security vulnerability where attackers inject malicious scripts into web pages that are viewed by other users.
42. Explain SQL Injection.
    • Answer: SQL Injection is a technique where an attacker inserts malicious SQL code into a query, potentially gaining unauthorized access to a database.

.NET Core and .NET 5/6:

43. What is the difference between .NET Core and .NET 5/6?
    • Answer: .NET Core is the predecessor of .NET 5/6, which is the unified platform that combines .NET Framework, .NET Core, and Xamarin.
44. Explain the concept of self-contained executables in .NET Core.
    • Answer: Self-contained executables include the runtime and libraries, allowing applications to be deployed without requiring a separate runtime installation.

Future Trends:

45. What are some features introduced in C# 9.0 and C# 10.0?
    • Answer: C# 9.0 introduced features like records, top-level statements, and pattern matching improvements. C# 10.0 introduced interpolated strings as format strings and improved pattern matching.