C# Programming Introduction

What You’ll Learn

This page is a self-contained introduction to C# (pronounced “C sharp”)—no prior coding experience required. You will understand what C# is, write your first console program, and learn how .NET runs your code.

🤔 What is C# Programming?

C# is a modern, multi-paradigm programming language developed by Microsoft. It is designed to be simple, efficient, and type-safe. Developers use it to build Windows desktop apps, web APIs with ASP.NET, cloud services on Azure, games with Unity, and cross-platform mobile apps with .NET MAUI.

C# is an object-oriented language. You organize code into classes and objects, which makes large applications easier to maintain, test, and extend. The .NET runtime manages memory for you through garbage collection, so you focus on logic rather than manual allocation.

👤 Who Created C#?

Anders Hejlsberg is widely considered the father of C#. The Danish computer scientist led the team at Microsoft that designed C# in the late 1990s, with the first release shipping alongside .NET in the early 2000s. The goal was a modern, object-oriented language for the Microsoft ecosystem that felt familiar to C++ and Java developers.

Since then, C# has evolved through many versions with generics, LINQ, async/await, records, and more. The timeline below highlights major milestones.

🔓 Is C# Open Source?

Yes. C# and .NET are open source. The Roslyn compiler, large parts of the runtime, and the base class libraries are available on GitHub under permissive licenses (MIT and similar). Developers can use, study, modify, and contribute to the platform freely.

You do not need Windows to write C# today—install the .NET SDK on Linux, macOS, or Windows and use VS Code, Visual Studio, or JetBrains Rider.

📝 Program Structure & Syntax

A classic C# console program includes a using directive, a class, and a Main method as the entry point:

using System;

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

Syntax rules

• using System; — imports the System namespace so you can use Console and other core types.
• class — defines a type that groups methods and data (object-oriented design).
• static void Main — entry point; the runtime calls this method when the program starts.
• Console.WriteLine — prints a line of text to the terminal.
• Semicolons — end statements; braces { } define blocks.
• Top-level statements — newer templates allow shorter Program.cs without an explicit class; both styles are valid.

💻 How to Create and Run a C# Program

Install the .NET SDK, then create a console project from a terminal:

dotnet new console -n HelloApp
cd HelloApp
dotnet run

• dotnet new console — scaffolds a project with Program.cs and a .csproj file.
• dotnet run — compiles and executes in one step (great while learning).
• dotnet build — compile only; useful before deployment.
• IDEs — Visual Studio, VS Code with C# Dev Kit, or JetBrains Rider provide IntelliSense and debugging.

🧰 Core Building Blocks

As you continue learning C#, these are the main ideas you will encounter:

Examples Gallery

Five starter console programs. Create a project with dotnet new console, paste into Program.cs (adjust class structure if needed), and run with dotnet run.

using System;

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

Hello, World!

using System;

class Vars
{
    static void Main()
    {
        int age = 20;
        double gpa = 3.85;
        char grade = 'A';
        string name = "Alex";

        Console.WriteLine($"Name: {name}");
        Console.WriteLine($"Age: {age}");
        Console.WriteLine($"GPA: {gpa:F2}");
        Console.WriteLine($"Grade: {grade}");
    }
}

Name: Alex
Age: 20
GPA: 3.85
Grade: A

using System;

class InputDemo
{
    static void Main()
    {
        Console.Write("Enter a number: ");
        string text = Console.ReadLine();
        int num = int.Parse(text);
        Console.WriteLine($"You entered: {num}");
    }
}

Enter a number: 42
You entered: 42

using System;

class AddDemo
{
    static int Add(int a, int b)
    {
        return a + b;
    }

    static void Main()
    {
        Console.WriteLine($"Sum = {Add(3, 5)}");
    }
}

Sum = 8

using System;

class EvenOdd
{
    static void Main()
    {
        Console.Write("Enter n: ");
        int n = int.Parse(Console.ReadLine());

        if (n % 2 == 0)
            Console.WriteLine($"{n} is even");
        else
            Console.WriteLine($"{n} is odd");
    }
}

Enter n: 7
7 is odd

📚 Why Learn C#?

• Versatile career path — web, desktop, games, cloud, and enterprise backends.
• Strong tooling — IntelliSense, debugging, and NuGet packages speed up development.
• Type safety — catch many errors at compile time before users see them.
• Modern language — regular updates add productivity features without breaking the ecosystem.
• Cross-platform .NET — deploy the same skills on Windows, Linux, and macOS.
• Unity & games — one of the most popular languages for indie and AAA game scripting.

Summary

• C# (C sharp) is a modern, type-safe language created by Anders Hejlsberg at Microsoft.
• It is object-oriented and runs on the cross-platform .NET runtime.
• C# and Roslyn are open source with an active community.
• Programs use using, classes, Main, and Console for basic I/O.
• Run locally with dotnet new console and dotnet run.
• The # symbol is the “sharp” in the name—like musical notation for a half-step higher.

💡 Best Practices