ASP.NET Core for C# (.NET): Complete Guide with Examples

What is ASP.NET Core and why is it needed?

ASP.NET Core is a modern, cross-platform, high-performance open-source web framework from Microsoft, designed for creating web applications, APIs, microservices, and cloud solutions in C# (.NET). Unlike classic ASP.NET (Framework), which only worked on Windows, ASP.NET Core is fully cross-platform: it runs on Windows, Linux, and macOS.

Why is it needed? ASP.NET Core provides developers with a powerful toolkit for building modern web applications. It includes built-in support for Dependency Injection, middleware, routing, authentication, database work via Entity Framework Core, and much more. The framework is optimized for high performance and scalability, making it an ideal choice for creating both small websites and large enterprise systems.

Key advantages of ASP.NET Core:

• Cross-platform: Runs on Windows, Linux, and macOS.
• High performance: One of the fastest web frameworks.
• Modularity: You only include the components your application needs.
• Built-in Dependency Injection support: Simplifies testing and code maintenance.
• Open Source: Source code is available on GitHub, the community actively develops the framework.
• Unified programming model: You can create MVC applications, Web API, Razor Pages, Blazor, and SignalR.

Installing ASP.NET Core

To get started with ASP.NET Core, you need to install the .NET SDK (Software Development Kit). This is not a package installed via pip or npm, but a full development environment.

Installation steps:

1. Download the .NET SDK: Go to the official website dotnet.microsoft.com/download and download the latest version of the .NET SDK for your operating system (Windows, Linux, macOS).
2. Install the SDK: Run the installer and follow the instructions. After installation, restart your computer (or terminal).
3. Verify the installation: Open a terminal (command line) and run the command:

   dotnet --version

   If you see a version number (e.g., 8.0.100), the installation was successful.

After installing the SDK, you will have access to the dotnet command, which is used to create, build, and run projects.

Quick start with a code example

Let's create a simple ASP.NET Core web application (Web API) that will return "Hello, World!".

Step 1: Create the project

Open a terminal and run the command:

dotnet new webapi -n MyFirstApicd MyFirstApi

This command will create a new Web API project named MyFirstApi and navigate into its folder.

Step 2: Project structure

In the project folder, you will see several files. The main ones are:

• Program.cs — the application entry point, where the request processing pipeline is configured.
• MyFirstApi.csproj — the project file containing dependencies and build settings.
• Controllers/ — the folder for controllers (by default, it already contains WeatherForecastController.cs).

Step 3: Run the application

Execute the command in the terminal:

dotnet run

After running, you will see a message that the application is running on http://localhost:5xxx (the port may differ). Open a browser and navigate to http://localhost:5xxx/weatherf