05·First sketch: Blink and the setup()/loop() structure

Introduction

Blink is the "Hello World" of Arduino: blinking the built-in LED. This lesson dissects it line by line and shows the skeleton that EVERY sketch has — two mandatory functions: void setup() run once at startup and void loop() repeated forever. You will learn pinMode(), digitalWrite(), delay(), the LED_BUILTIN constant, and the HIGH/LOW constants as values in code. We also cover C/C++ syntax basics (semicolons, curly braces, the void keyword) and common beginner pitfalls: a missing pinMode, a forgotten semicolon, a blocking delay, and swapping HIGH with LOW. We do not cover compilation or upload (that is lesson 4) or detailed pin anatomy (lesson 2).