04·The workflow: writing → compilation → upload

Introduction

Every Arduino task is the same loop: you write a sketch, compile it (Verify, the ✓ icon), then upload it to the board (Upload, the → icon). This lesson dissects what exactly happens under the hood: how a .ino sketch turns into a .hex file through preprocessing, avr-gcc compilation and linking, how Verify differs from Upload, how avrdude and the bootloader cooperate during a serial upload, and how to tell a compilation error apart from an upload error. We do not cover setup()/loop() syntax or the actual Blink here — that is lesson 5.