// oneline comment
/*
  multiline
  comment
*/

void setup() {
  pinMode(0, OUTPUT); // set up pin number 0 to be output
  pinMode(1, OUTPUT); // set up pin number 0 to be output
}

void loop() {
  digitalWrite(0, HIGH); // put pin 0 to high (5V in this case)
  delay(1000);
  digitalWrite(1, HIGH); // put pin 0 to high (5V in this case)
  delay(1000);
  digitalWrite(1, LOW); // put pin 1 to low (0V in this case)
  delay(1000);
  digitalWrite(0, LOW); // put pin 0 to low (0V in this case)
  delay(1000);
}