Day 1: Introduction to C# & .NET setup

Welcome to Day 1 of your 30-day journey into C# and ASP.NET Core.

If you’re coming from JavaScript, Python, or Ruby, stepping into the compiled, strongly typed world of C# might seem intimidating. But modern C# (.NET 8 and beyond) is incredibly fast, expressive, and a joy to write. It runs everywhere: Windows, Linux, Mac, and the cloud.

Today we’ll write our first program.

Setup

First, let’s get our tools. You need the .NET SDK.

1. Head over to dotnet.microsoft.com/download
2. Download and install the latest .NET SDK (e.g., .NET 8 or newer).
3. Open a terminal and run dotnet --version to ensure it installed correctly.

For your editor, Visual Studio Code (VS Code) with the C# Dev Kit extension is strictly recommended for modern cross-platform development.

Your First App

We will create a simple console application.

Open your terminal in an empty folder and run:

dotnet new console -n HelloWorld
cd HelloWorld

Open this folder in VS Code. You’ll see a Program.cs file.

Program.cs

Thanks to Top-Level Statements in modern C#, your Program.cs file doesn’t need all the boilerplate classes and methods it used to. It’s just one line!

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

Running It

To run the application, type this in the terminal:

dotnet run

You should see Hello, World! printed to the screen!

Analyzing the anatomy

What actually happened here?

1. dotnet run triggered the compiler (Roslyn).
2. The code was compiled into an Intermediate Language (IL) inside a .dll file.
3. The .NET Runtime took that IL, compiled it down to machine code instantly (Just-In-Time compiling), and ran it.

Console is a class built into .NET, and WriteLine is a method on that class that prints a string and a new line to the standard output.

Challenge for Day 1

1. Modify the Program.cs to ask for the user’s name using Console.ReadLine().
2. Print out a personalized greeting using String Interpolation (e.g. $"Hello {name}!").

Tomorrow: Variables, Types and Type Conversion.