📝 Lesson 1.3: Your First C# Program

The "Hello, World!" Tradition

For decades, the very first program people write in a new language does one simple thing: it displays the message "Hello, World!" on the screen. It's a tiny program, but it proves something important — that your tools work and you can go from writing code to running code.

That round trip is the heartbeat of programming:

Let's make that loop real. Open a terminal (or VS Code's built-in terminal) and, if you made the csharp-course folder in the last lesson, move into it:

cd csharp-course

Creating a Project

A C# program lives inside a project — a folder with your code plus a small file describing how to build it. The dotnet command can scaffold one for you.

Using the terminal (VS Code and everyone)

Run this command to create a new console project (a program that runs in a text window) named HelloWorld:

dotnet new console -o HelloWorld

Let's decode that command:

• dotnet new — "create a new project."
• console — the template to use: a console application.
• -o HelloWorld — "output it into a new folder named HelloWorld." (-o is short for "output.")

Now move into the new project folder and open it in your editor:

cd HelloWorld
code .

Using Visual Studio (Windows)

Anatomy of a Project

Look inside the HelloWorld folder. Ignoring the auto-generated bin and obj folders (temporary build output), you'll see two important files:

Open Program.cs. Depending on your .NET version, it will look something like this:

// See https://aka.ms/new-console-template for more information
Console.WriteLine("Hello, World!");

That's a complete, runnable program! Modern C# uses top-level statements, which let a simple program be just the lines that do the work — no extra scaffolding required. (We'll see the older, longer form in a moment, because you'll encounter it in other people's code.)

Building and Running It

From inside the HelloWorld folder, run:

dotnet run

The dotnet run command does two jobs at once: it builds (compiles) your code and then runs the result. After a moment you'll see:

Hello, World!

🎉 That's it — you just wrote and ran a C# program!

A Line-by-Line Code Tour

Let's understand exactly what you ran. Here's the program again:

// See https://aka.ms/new-console-template for more information
Console.WriteLine("Hello, World!");

Line 1 — the comment

Anything after // on a line is a comment: a note for humans that the compiler completely ignores. Comments explain why code does something. You can safely delete this line.

Line 2 — the statement

This single line is doing several things. Let's break it into pieces:

💡 Read it out loud: "Console, write this line: Hello, World!" That's genuinely all it says.

The longer, "traditional" form

You'll often see beginner programs written in this fuller style. It does the exact same thing as the two-line version — the top-level version just hides this scaffolding for you:

using System;

namespace HelloWorld
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("Hello, World!");
        }
    }
}

Don't worry about memorizing this now — we'll unpack namespace, class, and Main in later modules. For now, just recognize that both forms are the same program, and that Main is the official "starting point" where a program begins running.

Make It Your Own

The best way to learn is to change things and see what happens. In Program.cs, replace the code with this:

Console.WriteLine("Hello, World!");
Console.WriteLine("My name is Ada.");
Console.WriteLine("I am learning C#!");

Save the file, then run it again:

dotnet run

Hello, World!
My name is Ada.
I am learning C#!

Notice that each Console.WriteLine prints on its own line, and the program runs the statements top to bottom, in order. That ordering is fundamental: a program is a sequence of steps, carried out one after another.

Exercise & Quiz

// TODO: Make this print four lines about you
Console.WriteLine("--------------------");
Console.WriteLine("Name: ");
// Add more lines here...
Console.WriteLine("--------------------");

Console.WriteLine("--------------------");
Console.WriteLine("Name: Ada Lovelace");
Console.WriteLine("Hobby: Playing the piano");
Console.WriteLine("Learning C# to: build my own apps");
Console.WriteLine("Goal: Finish this course!");
Console.WriteLine("--------------------");

--------------------
Name: Ada Lovelace
Hobby: Playing the piano
Learning C# to: build my own apps
Goal: Finish this course!
--------------------

Summary

📚 Additional Resources

• Create a C# console app with VS Code — Microsoft Docs
• The dotnet run command — reference
• Top-level statements — Microsoft Docs

🚀 What's Next?

You can now create, run, and edit programs — that completes Module 1! In Module 2, we start with the real building blocks of programming. First up, Lesson 2.1: Variables and Data Types, where your programs start to remember and work with information.