Getting Started with C

C# is a statically typed, object-oriented language from Microsoft that runs on .NET, an open-source, cross-platform runtime. The same language and toolchain cover command-line tools, web APIs, desktop apps, Unity games, and cloud services. In this chapter you will install the .NET SDK, create and run a first project, look inside the project file, and set up an editor.

Installing the .NET SDK

To build C# code you need the .NET SDK. It bundles the compiler, the dotnet command-line tool, the base class libraries, and the runtime. Machines that only run apps can get by with the runtime alone, but your development machine needs the full SDK.

• Download installers for Windows, macOS, and Linux from the .NET download page. Unless you have a reason not to, pick the current long-term support (LTS) release.
• Package managers work too: winget on Windows, Homebrew on macOS, and your distribution's package manager or Microsoft's package feed on Linux.
• Installing Visual Studio with the .NET development workload also installs the SDK.

Open a fresh terminal afterwards and check the installation:

dotnet --version
dotnet --list-sdks
dotnet --info

dotnet --version prints the SDK currently in use, and dotnet --list-sdks shows every installed SDK. Multiple SDKs can live side by side; each project declares which framework version it targets.

Your First Project

dotnet new scaffolds projects from templates. The console app template is called console:

dotnet new console -o HelloApp
cd HelloApp
dotnet run

The -o HelloApp option creates a HelloApp folder and puts the project inside it. You get two files, HelloApp.csproj and Program.cs, and dotnet run prints Hello, World!. The whole program is a single line:

// Program.cs
Console.WriteLine("Hello, World!");

There is no class and no Main method because of top-level statements: the compiler generates the entry point around the statements in this file for you. Command-line arguments arrive in a predefined args variable:

if (args.Length == 0)
{
    Console.WriteLine("Usage: dotnet run -- <name>");
    return;
}

var name = args[0];
Console.WriteLine($"Hello, {name}! Today is {DateTime.Now:yyyy-MM-dd}.");

Run it with dotnet run -- Alice. Everything after -- is passed to your program; options before it belong to dotnet run itself.