How C# Code Works

Understanding how C# code works is fundamental to becoming an effective .NET developer. Let me break down the entire process from writing code to execution.

Compilation Process & Runtime Behavior

1. Source Code Creation

• Developers write C# code in .cs files.
• Code is structured within namespaces, classes, and methods.

Example:

using System;

class Program
{
    static void Main()
    {
        Console.WriteLine("Hello, World!");
    }
}

using System;

class Program
{
    static void Main()
    {
        Console.WriteLine("Hello, World!");
    }
}

2. Compilation Process

• The C# compiler (csc) compiles the code into Intermediate Language (IL).
• IL is CPU-independent and platform-agnostic.
• Output: Assembly (.exe or .dll) containing:
  • IL code
  • Metadata (type info, versioning, etc.)
  • Manifest (assembly identity)

3. Execution & Runtime Behavior

• The assembly runs on the .NET CLR (Common Language Runtime).

Key Steps:

1. Loading: The CLR loads the assembly into memory.
2. JIT Compilation: The Just-In-Time (JIT) compiler converts IL into native machine code.
3. Execution: Native code is executed by the CPU.

4. CLR Runtime Services

🔄 Complete Lifecycle Summary

Development Time:
[You Write C# Code] 
        ↓

Compile Time:
[C# Compiler] → [IL Code + Metadata] → [Assembly (.exe/.dll)]
        ↓

🟢 RUNTIME STARTS HERE - CLR TAKES CONTROL:
[CLR Loads Assembly] 
        ↓
[CLR JIT Compiles IL to Native Code]
        ↓
[CLR Executes Native Code]
        ↓
[CLR Provides Runtime Services]:
    • Garbage Collection
    • Type Safety Checks  
    • Exception Handling
    • Thread Management
    • Security Verification
        ↓
[Program Ends - CLR Shuts Down]

Development Time:
[You Write C# Code] 
        ↓

Compile Time:
[C# Compiler] → [IL Code + Metadata] → [Assembly (.exe/.dll)]
        ↓

🟢 RUNTIME STARTS HERE - CLR TAKES CONTROL:
[CLR Loads Assembly] 
        ↓
[CLR JIT Compiles IL to Native Code]
        ↓
[CLR Executes Native Code]
        ↓
[CLR Provides Runtime Services]:
    • Garbage Collection
    • Type Safety Checks  
    • Exception Handling
    • Thread Management
    • Security Verification
        ↓
[Program Ends - CLR Shuts Down]

🧠 Key Concepts to Remember

• C# code is compiled, not interpreted.
• The .NET CLR abstracts platform dependencies.
• The JIT compiler ensures efficient native execution.
• Managed code benefits from safety, performance, and productivity features.