初めてのArduino(Lチカまで) ref: https://qiita.com/h-sakano/items/ae57617f06a107bee3f3

file0.c

int led = 13;

void setup() {
  // put your setup code here, to run once:
  pinMode(led, OUTPUT);
}

void loop() {
  // put your main code here, to run repeatedly:
  digitalWrite(led, HIGH);
  delay(1000);
  digitalWrite(led, LOW);
  delay(1000);
}