What is C#, CLR/.NET, JIT vs AOT, SDK & dotnet CLI
Understand what C# and .NET are, how CLR executes IL, the difference between JIT and AOT, and how to use the SDK and dotnet CLI to run a first app.
What is C#, CLR/.NET, JIT vs AOT, SDK & dotnet CLI is a free C# Academy lesson on CoddyKit — lesson 1 of 3. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the C# Academy learning path, one of 3 lessons in the course, and your progress syncs across the web and the CoddyKit app.
Intro to C# & .NET
C# is a modern, type-safe language that runs on the cross-platform .NET platform.
- Great for web, desktop, mobile, games, and services
- Open-source tooling and libraries
- Focus on productivity and safety
CLR & IL overview
The CLR (Common Language Runtime) executes IL (Intermediate Language) with services like garbage collection, type safety, and exceptions.
- Compile C# → IL
- CLR loads IL and manages execution
JIT vs AOT
JIT compiles IL to native code at runtime; AOT compiles ahead of time.
- JIT: fast builds, adaptive optimization
- AOT: faster startup, smaller runtime deps
SDK & CLI basics
Install the .NET SDK to get the dotnet CLI.
- dotnet --info shows versions
- dotnet new console creates a project
- dotnet build and dotnet run compile and execute
Project layout & restore
A console app typically has a .csproj, Program.cs, and folders for code/tests.
- dotnet restore fetches NuGet packages
- Keep small files and clear names
Your first program
Here is a minimal console app using a Program class and Main. Keep code simple and readable.
using System;
public class Program
{
// Entry point: the runtime calls Main
public static void Main(string[] args)
{
// Print a friendly greeting
Console.WriteLine("Hello, C# from CoddyKit!");
// Tiny arithmetic example
int a = 2;
int b = 3;
Console.WriteLine("Sum = " + (a + b));
// String interpolation example
string name = "Ada";
Console.WriteLine($"Hi {name}, welcome!");
}
}
JIT definition
Quick check: Which option best describes JIT compilation in .NET?
Recap
Recap: C# runs on .NET's CLR; JIT compiles IL at runtime; AOT precompiles; the dotnet CLI builds and runs your app.
Frequently asked questions
Is the “What is C#, CLR/.NET, JIT vs AOT, SDK & dotnet CLI” lesson free?
Yes — the full text of “What is C#, CLR/.NET, JIT vs AOT, SDK & dotnet CLI” is free to read here on the web, and the C# Academy course includes 3 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the C# Academy course, upgrade to CoddyKit PRO.
What will I learn in “What is C#, CLR/.NET, JIT vs AOT, SDK & dotnet CLI”?
Understand what C# and .NET are, how CLR executes IL, the difference between JIT and AOT, and how to use the SDK and dotnet CLI to run a first app. You practise C# Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start C# Academy?
No prior experience is required. C# Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 1 of 3, so you can start here or from the beginning and move at your own pace.
How long does the “What is C#, CLR/.NET, JIT vs AOT, SDK & dotnet CLI” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this C# Academy lesson?
Yes. Every C# Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- What is C#, CLR/.NET, JIT vs AOT, SDK & dotnet CLI
- First Program: top-level statements vs Program class; build & run
- Project layout, NuGet restore, debugging basics