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Day 01Sprint 1 • C# 12 & .NET CLI
2 Hours

Day 1: .NET 9 SDK, VS Code C# Dev Kit & First CLI App

.NET 9 is Microsoft's flagship high-performance, cross-platform runtime for modern cloud, web, and desktop systems. With C# 12 top-level statements, unnecessary boilerplate is eliminated, allowing developer code to execute directly with minimal syntax.

Install .NET 9 SDK and verify dotnet --info in terminal
Configure Visual Studio Code with the official C# Dev Kit extension
Create a modern C# 12 console application using dotnet new console
Understand Top-Level Statements and build your first CLI greetings engine
💡 Simple English Theory of .NET

What is this in Simple, Everyday English?

.NET 9 is Microsoft's flagship high-performance, cross-platform runtime for modern cloud, web, and desktop systems. With C# 12 top-level statements, unnecessary boilerplate is eliminated, allowing developer code to execute directly with minimal syntax.

⚙️ Under The Hood: How .NET Executes This Code

Ever wondered what happens behind the scenes when you run dotnet run? Here is the step-by-step internal workflow:

11. Roslyn C# Compiler: Takes your readable C# code and compiles it into MSIL (Microsoft Intermediate Language) bytecode.
22. Common Language Runtime (CLR): The virtual machine environment that loads your assembly (.dll) and manages memory safely.
33. RyuJIT (Just-In-Time) Compiler: Compiles IL bytecode into native 64-bit machine CPU instructions right before execution.
44. Automatic Garbage Collector (GC): Automatically tracks and cleans up objects in RAM (Gen 0, 1, 2) with zero manual memory leaks.

🎯 Core Key Points to Master

  • .NET 9 SDK includes compiler, runtime, CLI tools, and Base Class Libraries (BCL)
  • Top-level statements eliminate the classic class Program { static void Main() } ceremony
  • dotnet run compiles in-memory and launches the application instantly
  • dotnet build creates binary outputs in bin/Debug/net9.0/

💡 Real-World Developer Analogy

Think of .NET 9 runtime as an ultra-fast Formula-1 engine. C# is the steering wheel, and the dotnet CLI is your command dashboard to start, test, and tune the vehicle.

🏢 Why Companies & Tech Giants Use This in .NET

.NET is trusted by high-scale companies like Microsoft, Stack Overflow, and banking institutions because it combines lightning-fast execution speed with strict compile-time type safety and cross-platform Docker cloud deployment.

⚠️ Beginner Trap to Avoid

Avoid blocking asynchronous Tasks with .Result or .Wait() — always use 'await' all the way down to avoid thread pool starvation and freezing your application.

Day 2: C# Type System, Nullable Types & Pattern Matching