As the demand for skilled C# developers continues to grow, it is essential for job seekers to be well-prepared for the interview process. To help you in your preparation, we have compiled a list of 85 must-know C# interview questions and answers that you should be familiar with in 2024.
1. What is C#?
Answer: C# is a modern, object-oriented programming language developed by Microsoft as part of the .NET framework.
2. What are the key features of C#?
Answer: Some key features of C# include type safety, garbage collection, events and delegates, and LINQ (Language Integrated Query).
3. What is the difference between value types and reference types in C#?
Answer: Value types store their data directly in memory, whereas reference types store a reference to the data in memory.
4. What is the difference between a class and a struct in C#?
Answer: Classes are reference types and are allocated on the heap, while structs are value types and are allocated on the stack.
5. What is a namespace in C#?
Answer: A namespace is a way to organize and provide a scope for classes and other types in C#.
6. What is the difference between abstract classes and interfaces in C#?
Answer: Abstract classes can have both abstract and non-abstract methods, while interfaces can only have abstract methods.
7. What is the significance of the “using” statement in C#?
Answer: The “using” statement in C# is used for automatic resource management, such as closing a file or database connection when it is no longer needed.
8. What is the difference between the “readonly” and “const” keywords in C#?
Answer: The “readonly” keyword is used to create read-only fields that can be initialized at runtime, while the “const” keyword is used to create compile-time constants.
9. What is the purpose of the “as” and “is” operators in C#?
Answer: The “as” operator is used for casting objects, while the “is” operator is used for type checking.
10. What is the difference between “out” and “ref” parameters in C#?
Answer: “out” parameters are used for returning multiple values from a method, while “ref” parameters are used for passing arguments by reference.
11. What is Boxing and Unboxing in C#?
Answer: Boxing is the process of converting a value type to a reference type, while Unboxing is the process of converting a reference type back to a value type.
12. What is the purpose of the “finally” block in a try-catch-finally statement in C#?
Answer: The “finally” block is used for executing code that should always run, regardless of whether an exception is thrown or not.
13. How does C# handle exceptions?
Answer: C# uses try-catch-finally blocks to handle exceptions, allowing developers to gracefully handle errors and prevent their application from crashing.
14. What is the difference between an interface and an abstract class in C#?
Answer: Interfaces can only contain method signatures and properties, while abstract classes can contain both abstract and concrete methods.
15. How does C# support multi-threading?
Answer: C# supports multi-threading through the System.Threading namespace, which provides classes and interfaces for creating and managing threads.
16. What is the purpose of the “Task” class in C#?
Answer: The “Task” class in C# is used for asynchronous programming, allowing developers to perform tasks in parallel without blocking the main thread.
17. What is the difference between a delegate and an event in C#?
Answer: A delegate is a type that references a method, while an event is a mechanism for notifying subscribers when an action occurs.
18. What is LINQ (Language Integrated Query) in C#?
Answer: LINQ is a feature in C# that allows developers to query data from different sources using a SQL-like syntax.
19. How does C# support data serialization?
Answer: C# supports data serialization through the System.Runtime.Serialization namespace, which provides classes for serializing and deserializing objects.
20. What is the difference between an abstract class and a sealed class in C#?
Answer: An abstract class cannot be instantiated and must be inherited from, while a sealed class cannot be inherited from.
21. What is the purpose of the “using” directive in C#?
Answer: The “using” directive in C# is used to import namespaces so that their types can be used without fully-qualified names.
22. What is the difference between shadowing and overriding in C#?
Answer: Shadowing is the process of redefining a member in a derived class, while overriding is the process of providing a new implementation for a virtual or abstract member.
23. What is the purpose of the “volatile” keyword in C#?
Answer: The “volatile” keyword in C# is used to indicate that a field can be modified by multiple threads and should not be cached.
24. What is the difference between “var” and “dynamic” in C#?
Answer: The “var” keyword is used for implicit type inference at compile time, while the “dynamic” keyword is used for dynamic type checking at runtime.
25. What is the purpose of the “yield” keyword in C#?
Answer: The “yield” keyword is used for creating iterators, allowing developers to simplify the process of iterating over collections.
26. What is an extension method in C#?
Answer: An extension method is a static method that can be called as if it were an instance method of a class, adding functionality to existing types without modifying them.
27. What is the purpose of the “params” keyword in C#?
Answer: The “params” keyword in C# is used to specify a variable number of parameters for a method, allowing developers to pass in an array of arguments.
28. What is the difference between the “lock” and “Monitor” classes in C#?
Answer: The “lock” keyword is a shortcut for using the “Monitor” class to create a mutual-exclusion lock on an object.
29. What is the difference between “async” and “await” in C#?
Answer: The “async” keyword is used to mark a method as asynchronous, while the “await” keyword is used to asynchronously wait for a task to complete.
30. What is the purpose of the “Task.Delay” method in C#?
Answer: The “Task.Delay” method in C# is used to asynchronously delay the execution of a method for a specified amount of time.
31. What is the purpose of the “Lazy” class in C#?
Answer: The “Lazy” class in C# is used for lazy initialization, allowing developers to defer the creation of an object until it is needed.
32. What is the difference between “Response.Redirect” and “Server.Transfer” in C#?
Answer: “Response.Redirect” sends an HTTP redirect response to the client, while “Server.Transfer” transfers processing to another ASP.NET page on the server.
33. What is the purpose of the “ViewState” in ASP.NET and how is it persisted?
Answer: The “ViewState” in ASP.NET is used to persist control state information across postbacks by serializing it into a hidden field on the page.
34. What is the difference between a server control and a user control in ASP.NET?
Answer: Server controls are reusable components that are defined in the WebForms page, while user controls are reusable components that are defined in separate ASCX files.
35. What is the purpose of the “Web.config” file in ASP.NET?
Answer: The “Web.config” file in ASP.NET is used to configure settings for the application, such as connection strings, session state, and authentication.
36. What is the difference between a static and an instance method in C#?
Answer: Static methods are called on the class itself, while instance methods are called on an instance of the class.
37. What is the purpose of the “is” and “as” operators in C#?
Answer: The “is” operator is used for type checking, while the “as” operator is used for casting objects.
38. What is the difference between ‘ref’ and ‘out’ parameters in C#?
Answer: ‘ref’ parameters must be initialized before passing them to a method, while ‘out’ parameters do not need to be initialized and are used for returning values.
39. What is the difference between a List and an ArrayList in C#?
Answer: A List is a strongly-typed collection that is faster and more efficient compared to an ArrayList, which is a non-generic collection.
40. What is the purpose of the “using” statement in C#?
Answer: The “using” statement in C# is used for automatically disposing of resources, such as file streams and database connections.
41. What is the difference between an interface and an abstract class in C#?
Answer: An interface can only contain method signatures, while an abstract class can contain both abstract and concrete methods.
42. What is the difference between a value type and a reference type in C#?
Answer: Value types are stored on the stack, while reference types are stored on the heap.
43. What is the purpose of the “finally” block in a try-catch-finally statement in C#?
Answer: The “finally” block is used for executing code that should run regardless of whether an exception is thrown or not.
44. What is the significance of the “static” keyword in C#?
Answer: The “static” keyword is used to declare members that belong to the class itself, rather than to instances of the class.
45. What is the purpose of the “virtual” and “override” keywords in C#?
Answer: The “virtual” keyword is used to mark a method for overriding in a derived class, while the “override” keyword is used to override a base class method.
46. What is polymorphism in C#?
Answer: Polymorphism is the ability of objects to take on multiple forms, allowing them to be treated as instances of their base class or as instances of their derived classes.
47. What is the difference between a function and a method in C#?
Answer: A method is a member of a class, while a function is a standalone block of code that can be called without an instance of a class.
48. What is the purpose of the “this” keyword in C#?
Answer: The “this” keyword in C# is used to refer to the current instance of a class or struct.
49. What is the difference between a private and a protected access modifier in C#?
Answer: A private member is accessible only within the containing class, while a protected member is accessible within the containing class and its derived classes.
50. What is the purpose of the “sealed” keyword in C#?
Answer: The “sealed” keyword in C# is used to prevent a class from being inherited.
51. What is a delegate in C#?
Answer: A delegate is a type that references a method, allowing developers to create callbacks and event handlers.
52. What is an event in C#?
Answer: An event is a mechanism for notifying subscribers when an action occurs, encapsulating delegates for method invocation.
53. What is the difference between an abstract class and an interface in C#?
Answer: An abstract class can contain both abstract and concrete methods, while an interface can only contain method signatures.
54. What is serialization in C#?
Answer: Serialization is the process of converting an object into a format that can be easily persisted or transmitted over a network.
55. What is the difference between serialization and deserialization in C#?
Answer: Serialization is the process of converting an object into a format that can be persisted or transmitted, while deserialization is the process of converting that format back into an object.
56. What is the purpose of the “enum” keyword in C#?
Answer: The “enum” keyword in C# is used to define a set of named constants, making code more readable and maintainable.
57. What is the difference between the “== ” and “Equals” operators in C#?
Answer: The “==” operator compares the reference of two objects, while the “Equals” method compares the values of two objects.
58. What is the difference between a shallow copy and a deep copy in C#?
Answer: A shallow copy copies the references of the members, while a deep copy duplicates the objects themselves.
59. What is the significance of the “using” directive in C#?
Answer: The “using” directive in C# is used to import namespaces so that their types can be used without fully-qualified names.
60. What is the difference between the “IEnumerable” and “IQueryable” interfaces in C#?
Answer: The “IEnumerable” interface is used for in-memory collection operations, while the “IQueryable” interface is used for queryable data sources such as databases.
61. What is the purpose of the “yield” keyword in C#?
Answer: The “yield” keyword is used for creating iterators, simplifying the process of iterating over collections.
62. What is dependency injection in C#?
Answer: Dependency injection is a design pattern in which the dependencies of a class are injected into it, rather than being created internally.
63. What is the purpose of the “async” and “await” keywords in C#?
Answer: The “async” keyword is used to mark a method as asynchronous, while the “await” keyword is used to asynchronously wait for a task to complete.
64. What is the difference between the “StringBuilder” and “String” classes in C#?
Answer: The “StringBuilder” class is mutable and is used for building strings efficiently, while the “String” class is immutable.
65. What is the difference between a stack and a queue in C#?
Answer: A stack is a last-in, first-out (LIFO) data structure, while a queue is a first-in, first-out (FIFO) data structure.
66. What is the difference between a binary search and a linear search in C#?
Answer: A binary search is more efficient and requires sorted data, while a linear search traverses the data sequentially.
67. What is the difference between a synchronous and an asynchronous method in C#?
Answer: A synchronous method blocks the main thread until it completes, while an asynchronous method does not block the main thread.
68. What is the purpose of the “using” statement in C#?
Answer: The “using” statement in C# is used for automatic resource management, such as closing file streams and database connections.
69. What is the difference between an aggregate and a standard query operator in LINQ?
Answer: Aggregates perform a transformation on a sequence or group of elements, while standard query operators filter and sort elements.
70. What is the purpose of the “request” and “response” objects in ASP.NET?
Answer: The “request” object contains information about the incoming HTTP request, while the “response” object is used to send a response back to the client.
71. What is the difference between a session and a cookie in ASP.NET?
Answer: A session is stored on the server and persists across multiple requests, while a cookie is stored on the client and persists until its expiration date.
72. What is the purpose of the “ViewData” and “ViewBag” objects in MVC?
Answer: The “ViewData” object is a dictionary that allows data to be passed between the controller and view, while the “ViewBag” is a dynamic property that allows data to be passed to the view.
73. What is the difference between “ModelState” and “ViewData” in MVC?
Answer: “ModelState” is used to validate and persist model state, while “ViewData” is used to pass data between the controller and view.
74. What is the difference between a GET and a POST request in ASP.NET?
Answer: A GET request retrieves data from the server, while a POST request sends data to the server for processing.
75. What is the purpose of the “appsettings.json” file in ASP.NET Core?
Answer: The “appsettings.json” file is used to store configuration settings for an ASP.NET Core application, such as connection strings and logging settings.
76. What is the difference between a view component and a partial view in ASP.NET Core?
Answer: A view component is a reusable component with its own logic and view, while a partial view is a reusable view that can be included in other views.
77. What is the purpose of the “UseHttpsRedirection” middleware in ASP.NET Core?
Answer: The “UseHttpsRedirection” middleware in ASP.NET Core is used to redirect HTTP requests to HTTPS for secure communication.
78. What is the difference between a singleton and a scoped service in ASP.NET Core?
Answer: A singleton service is created once per application, while a scoped service is created once per HTTP request.
79. What is the purpose of the “DbContext” class in Entity Framework Core?
Answer: The “DbContext” class in Entity Framework Core is used to represent a session with the database, allowing developers to query and save data.
80. What is the difference between “AddTransient”, “AddScoped”, and “AddSingleton” in ASP.NET Core Dependency Injection?
Answer: “AddTransient” creates a new instance each time it is requested, “AddScoped” creates a single instance per HTTP request, and “AddSingleton” creates a single instance per application.
81. What is the purpose of the “Authorize” attribute in ASP.NET Core?
Answer: The “Authorize” attribute in ASP.NET Core is used to restrict access to controller actions, requiring users to be authenticated.
82. What is the difference between “app.UseMvc()” and “app.UseRouting()” in ASP.NET Core?
Answer: “app.UseMvc()” sets up the MVC middleware for routing and controllers, while “app.UseRouting()” sets up routing for the application.
83. What is the benefit of using Entity Framework Core over traditional ADO.NET?
Answer: Entity Framework Core provides an object-relational mapping (ORM) framework that simplifies data access, reducing the amount of boilerplate code required.
84. What is the purpose of the “Include” method in Entity Framework Core?
Answer: The “Include” method in Entity Framework Core is used to include related entities in a query, preventing lazy loading.
85. What is the difference between the “First” and “FirstOrDefault” methods in LINQ?
Answer: “First” throws an exception if no element is found, while “FirstOrDefault” returns the default value (null for reference types) if no element is found.
In conclusion, preparing for a C# interview requires a good understanding of the language, its key features, and common programming concepts. By studying and practicing these 85 must-know C# interview questions and answers, you can improve your chances of landing your dream job in 2024. Good luck!
