C# Introduction

C# is a modern, object-oriented programming language that runs on the .NET platform.

What is C#?

C# was created by Microsoft and first released in 2002
It was designed by Anders Hejlsberg
It runs on .NET, which is free, open source and works on Windows, macOS and Linux
Its syntax looks like C, C++ and Java, so it is easy to move between them

What Can You Build?

Type of app	Tool
Websites and web APIs	ASP.NET Core
Games	Unity
Desktop apps	WPF, Windows Forms, WinUI
Mobile apps	.NET MAUI
Cloud services	Azure Functions

Setting Up

Download and install the free .NET SDK (choose the latest LTS version) from Microsoft's .NET website.
Install an editor: Visual Studio Community (Windows) or Visual Studio Code with the C# Dev Kit extension.
Open a terminal and create a new console project:

Example

text

dotnet new console -o HelloApp
cd HelloApp
dotnet run

Output

Hello, World!

The project contains a file named Program.cs. Open it and replace its code with your own.

Your First Program

Example

csharp

Console.WriteLine("Assalam o Alaikum!");
Console.WriteLine("Welcome to C# at Workownix.");

Output

Assalam o Alaikum!
Welcome to C# at Workownix.

Console.WriteLine prints text and moves to a new line. Console.Write prints without moving to a new line. Each statement ends with a semicolon ;.

The Classic Program Structure

The short form above is called top-level statements (C# 9 and later). Behind the scenes, C# wraps it in a class with a Main method. In older code and many books you will see the full form:

Example

csharp

using System;

namespace HelloApp
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("Hello from Main");
        }
    }
}

Output

Hello from Main

Part	Meaning
`using System;`	Lets you use classes like `Console` without writing `System.Console`
`namespace`	A named group that keeps your classes organised
`class Program`	A class that holds the code
`static void Main`	The method where the program starts

Comments

Example

csharp

// A single-line comment

/* A comment
   over several lines */
Console.WriteLine("Comments are ignored"); // also here

C# is case sensitive. Console.WriteLine works, but console.writeline is an error.

Exercise

Which command runs a C# console project from the terminal?

csharp rundotnet runnode Program.csrun Program.cs