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Introduction to C# and .NET

A beginner friendly introduction to C#, the .NET platform it runs on, where the language came from and what you can build with it.

Bishal Biswas

Bishal Biswas

Self Learner

Published on: April 1, 2026
Last updated: September 5, 2026
Beginner Topic

What is C#?

C# (pronounced “C sharp”) is a modern, general purpose programming language created by Microsoft. It is statically typed, which means the compiler checks your code before it runs, and it is object oriented, which means you organise code into classes and objects.

If you have written JavaScript or Python before, C# will feel familiar but stricter. The compiler catches a whole category of mistakes before your program ever starts.

What is .NET?

C# does not run on its own. It runs on .NET, a free, open source platform that provides:

  • The runtime (CLR): the engine that executes your compiled code, manages memory and handles errors.
  • The base class library: thousands of ready made classes for strings, files, networking, dates, collections and much more.
  • The SDK and tooling: the dotnet command line tool, compilers and project templates.

Think of C# as the language you write and .NET as everything that makes that writing run.

A very short history

  • 2000: C# 1.0 is announced alongside the first .NET Framework, led by Anders Hejlsberg.
  • 2005: C# 2.0 adds generics, the feature that makes List<T> possible.
  • 2007: C# 3.0 adds LINQ and lambda expressions.
  • 2012: C# 5.0 adds async and await.
  • 2016: .NET Core arrives, and C# becomes cross platform on Windows, macOS and Linux.
  • 2020 onwards: .NET 5, 6, 7, 8 and beyond unify everything into one platform with a yearly release.

The language you learn today is C# 12 and later, running on modern .NET. Anything called “.NET Framework” is the older Windows only version and you will rarely need it for new work.

What can you build?

C# is used in a surprising number of places:

  • Web apps and APIs with ASP.NET Core.
  • Desktop apps with WPF, WinUI and Avalonia.
  • Mobile apps with .NET MAUI.
  • Games with Unity, the most popular game engine in the world.
  • Cloud services on Azure and AWS.
  • Console tools and scripts for automation.

How C# code becomes a program

Here is the journey from source file to running program:

  1. You write code in a .cs file.
  2. The C# compiler turns it into Intermediate Language (IL), a portable set of instructions.
  3. At run time the CLR uses a Just In Time (JIT) compiler to turn IL into machine code for the CPU it is running on.

This two step process is why one build can run on Windows, macOS and Linux.

What C# code looks like

You do not need to understand every word yet. Just notice the shape.

// A tiny C# program
using System;

class Program
{
    static void Main()
    {
        // Print a message to the screen
        Console.WriteLine("Hello from C#!");

        // Declare a variable with a type
        int year = 2026;
        Console.WriteLine($"The year is {year}");
    }
}

A few things stand out:

  • Every statement ends with a semicolon.
  • Code lives inside braces { }.
  • Variables have a type, such as int.
  • Console.WriteLine prints text.

Top level statements

Modern .NET lets you skip the class and Main method wrapper for simple programs:

// The same program with top level statements
Console.WriteLine("Hello from C#!");

int year = 2026;
Console.WriteLine($"The year is {year}");

Both versions do the same thing. The compiler adds the wrapper for you. This course uses top level statements for short examples and full classes when the structure matters.

Quick recap

  • C# is a statically typed, object oriented language created by Microsoft.
  • .NET is the runtime and library platform that C# runs on, and it is free, open source and cross platform.
  • Code is compiled to IL and then JIT compiled to machine code when it runs.
  • C# powers web, desktop, mobile, game and cloud applications.
  • Top level statements let small programs skip the boilerplate.

In the next topic you will install the tools and get ready to write your own code.

Program.cs

// Program.cs - your first look at C#
using System;
class Program
{
    static void Main()
    {
        // 1. Printing to the console
        Console.WriteLine("Hello from C#!");
        // 2. Variables have a type
        int year = 2026;
        string language = "C#";
        // 3. String interpolation joins text and values
        Console.WriteLine($"Learning {language} in {year}");
        // 4. The compiler checks types before the program runs
        // int wrong = "text";   // this line would not compile
        // 5. .NET gives you a huge library for free
        Console.WriteLine(Math.Max(10, 42));          // 42
        Console.WriteLine(DateTime.Now.Year);         // current year
    }
}

Next

Setting Up Visual Studio and .NET SDK

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