Question 1

What is a variable in C#?

Accepted Answer

A variable is a named storage location in memory that holds a value which can be modified during program execution. Each variable has a type that determines what values it can contain and what operations are allowed. Declaring a variable with an explicit type allows the compiler to verify code consistency and optimize memory usage.

Question 2

What is a delegate in C#?

Accepted Answer

A delegate is a type that represents references to methods with a particular signature. It allows passing methods as parameters, storing them in variables, and invoking them dynamically. Delegates are the foundation of events and callbacks in C#, providing essential flexibility for event-driven programming and design patterns like Strategy or Observer.

Question 3

What is the correct syntax to declare a nullable int variable in C#?

Accepted Answer

In C#, a nullable type for value types is declared with the '?' suffix after the type (int?, bool?, DateTime?). This allows value types to have a null value, which is not possible by default. Nullable types are useful to represent the absence of value in database or API scenarios.

Question 4

What is a Controller in ASP.NET Core?

Accepted Answer

A Controller is a class that handles incoming HTTP requests and returns responses. It contains action methods (Actions) that process specific requests and generate content (HTML, JSON, etc.). Controllers inherit from ControllerBase for APIs or from Controller for MVC applications with views.

Question 5

What is a Minimal API in ASP.NET Core?

Accepted Answer

Minimal APIs are a simplified approach to creating HTTP APIs in ASP.NET Core, introduced with .NET 6. They allow defining endpoints directly in Program.cs without requiring controllers or complex configuration. This approach reduces boilerplate code and improves performance for simple to moderately complex APIs, while offering a more modern and functional development experience.

Question 6

Which REST principle requires that an API stores no session state between requests?

Accepted Answer

The statelessness principle requires that each request contains all necessary information to be processed. The server maintains no session context between calls. This improves scalability as requests can be handled by any server without state sharing.

Question 7

Why use async/await in ASP.NET Core controller actions?

Accepted Answer

Using async/await in controllers frees thread pool threads during I/O operations (database, external APIs). This improves server scalability by allowing the thread to process other requests while waiting. Without async, the thread remains blocked and consumes resources unnecessarily, limiting the number of concurrent requests.

Question 8

What is the Garbage Collector (GC) in .NET?

Accepted Answer

The Garbage Collector is an automatic memory management mechanism that frees unused objects on the managed heap. It runs automatically in the background to prevent memory leaks, unlike C/C++ where memory must be manually freed. The GC analyzes object references and collects those that are no longer accessible from application roots.

Question 9

What is the IObservable<T> interface in Reactive Extensions (Rx.NET)?

Accepted Answer

IObservable is the fundamental interface in Rx.NET that represents a push-based data source. It exposes a Subscribe method allowing observers to subscribe to receive asynchronous notifications. It's the reactive counterpart to IEnumerable: while IEnumerable pulls data synchronously, IObservable pushes data asynchronously to subscribers.

Question 10

What is the main role of the 'await' keyword in an asynchronous method?

Accepted Answer

The await keyword suspends the execution of the asynchronous method until the Task completes, while freeing the calling thread to process other tasks. This avoids thread blocking and improves application scalability. Unlike Task.Wait() or Task.Result which block the thread, await enables efficient use of thread pool resources.

.NET interview questions

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