C# interview questions

Here are some potential interview questions and answers for a C# developer with five years of experience:

Can you explain the difference between value types and reference types in C#?
In C#, value types are data types that store the data directly in the memory location allocated to the variable. These include data types like int, char, and bool. Reference types, on the other hand, store a reference to the data in memory, rather than the data itself. These include data types like objects, strings, and arrays.

How do you handle exceptions in C#?
In C#, exceptions are handled using the try-catch-finally block. The try block contains the code that might throw an exception, the catch block contains the code that handles the exception, and the finally block contains code that is always executed, whether or not an exception is thrown.

Can you explain the difference between an interface and an abstract class in C#?
An interface in C# defines a contract for a class, specifying a set of methods that the class must implement. An abstract class, on the other hand, is a class that cannot be instantiated and is typically used as a base class for other classes that implement its methods. An abstract class can have both abstract and non-abstract methods, whereas an interface can only have abstract methods.

Can you explain the difference between a static and an instance method in C#?
A static method in C# is a method that belongs to the class itself, rather than an instance of the class. This means that static methods can be called without creating an instance of the class. An instance method, on the other hand, is a method that belongs to an instance of a class, and must be called on an instance of the class to be executed.

Can you explain the concept of object-oriented programming, and how it is implemented in C#?
Object-oriented programming (OOP) is a programming paradigm that is based on the concept of "objects", which are data structures that contain both data and behavior. In OOP, objects interact with each other to perform tasks and achieve a desired outcome. In C#, OOP is implemented using various language features, including classes, objects, inheritance, polymorphism, and interfaces.

Can you explain the difference between a struct and a class in C#?
In C#, a struct is a value type that is used to represent a simple data structure. It is similar to a class, but it is stored on the stack rather than the heap, and it cannot be inherited from other classes. A class, on the other hand, is a reference type that can contain both data and behavior, and it can be inherited by other classes.

Can you explain the concept of generics in C#, and give an example of how they can be used?
In C#, generics are a language feature that allow you to define type-safe data structures without specifying the exact data type that they will contain. This allows you to create classes, interfaces, and methods that can work with any data type, while still maintaining type safety. For example, you could create a generic List class that can store a list of items of any data type, and the compiler would ensure that the items in the list are all of the same type.

Can you explain the concept of delegates and events in C#, and give an example of how they are used?
In C#, a delegate is a type that defines a reference to a method. It allows you to pass a method as an argument to another method, and to invoke the method dynamically at runtime. Events are a language feature that use delegates to provide a way for an object to notify other objects when a certain event occurs. For example, you could use a delegate and events to create a button control that can be clicked, and that will execute a custom method that you specify when it is clicked.

Can you explain the concept of asynchronous programming in C#, and give an example of how it is used?
In C#, asynchronous programming is a language feature that allows you to write code that can be executed concurrently with other code. This allows you to write more efficient and responsive applications, because it allows you to avoid blocking the main thread of execution while waiting for long-running operations to complete. For example, you could use asynchronous programming to make an HTTP request to a web server without blocking the user interface of your application, and handle the response when it arrives.

Can you explain the concept of LINQ in C#, and give an example of how it is used?
In C#, LINQ (Language-Integrated Query) is a language feature that allows you to write queries over data collections using a syntax that is similar to SQL. It provides a uniform way to query different data sources, including arrays, lists, and databases, using the same syntax and techniques. For example, you could use LINQ to query a collection of objects in memory and filter them based on a specific criteria, or to query a database and retrieve a set of records that match a specific condition.


Can you explain the concept of attributes in C#, and give an example of how they are used?
In C#, attributes are declarative elements that provide additional metadata about a program element, such as a class, method, or property. They allow you to annotate your code with additional information that can be used by other code or tools. For example, you could use attributes to mark a method as obsolete, to specify the name of the database table that a class maps to, or to apply validation rules to the parameters of a method.

Can you explain the difference between a constructor and a destructor in C#?
In C#, a constructor is a special method that is called when an instance of a class is created. It is used to initialize the instance, and it has the same name as the class. A destructor, on the other hand, is a special method that is called when an instance of a class is garbage collected. It is used to perform any necessary cleanup operations, and it has the same name as the class preceded by a tilde (~).

Can you explain the concept of garbage collection in C#, and how it works?
In C#, garbage collection is a mechanism that automatically manages the allocation and deallocation of memory for objects. It periodically checks for objects that are no longer in use, and frees the memory that they occupy to make it available for other objects. This ensures that the application does not run out of memory, and it allows the developer to focus on writing code, rather than managing memory directly.

Can you explain the concept of extension methods in C#, and give an example of how they are used?
In C#, extension methods are a language feature that allows you to add new methods to an existing type without modifying the type itself. This is done by defining a static method in a static class, and using the "this" keyword in the first parameter to specify the type that the method will extend. For example, you could use extension methods to add a "ToCamelCase" method to the string type, which would convert a string to camel case. This method could be called on any string object, as if it were a built-in method of the string type.

Can you explain the difference between a value type and a reference type in C#?
In C#, a value type is a data type that stores the data directly in the memory location allocated to the variable. These include data types like int, char, and bool. A reference type, on the other hand, stores a reference to the data in memory, rather than the data itself. These include data types like objects, strings, and arrays. The main difference between value types and reference types is that value types are copied when they are assigned to a new variable, whereas reference types are not. This means that changes made to a value type variable do not affect other variables, whereas changes made to a reference type variable can affect other variables that refer to the same object.