// the setup function runs once when you press reset or power the board
void setup() {
  // initialize digital pin 1-5 as an output.
  pinMode(1, OUTPUT);
  pinMode(2, OUTPUT);
  pinMode(3, OUTPUT);
  pinMode(4, OUTPUT);
  pinMode(5, OUTPUT);
  pinMode(0, OUTPUT);
  
}

int timer = 100;
const int pin_first = 1;
const int pin_last = 5;

void loop() {
  digitalWrite(0, HIGH);
  // loop from the lowest pin to the highest:
  for (int pin = 1; pin < 5; pin++) {
    // turn the pin on:
    digitalWrite(pin, HIGH);
    delay(timer);
    // turn the pin off:
    digitalWrite(pin, LOW);
  }

  digitalWrite(0, LOW);
  // loop from the highest pin to the lowest:
  for (int pin = 5; pin >= 1; pin--) {
    // turn the pin on:
    digitalWrite(pin, HIGH);
    delay(timer);
    // turn the pin off:
    digitalWrite(pin, LOW);
  }
}