int leds[8] = {2, 3, 4, 5, 6, 7, 8, 9};


void setup() {
  for(int i = 0; i < 8; i++) {
  pinMode(leds[i], OUTPUT);
  }
}

void loop() {
  // put your main code here, to run repeatedly:
  for(int i = 0; i < 8; i++){
    digitalWrite(leds[i], HIGH);
    delay(100);
  }

  for(int i = 0; i < 8; i++){
    digitalWrite(leds[i], LOW);
    delay(100);
  }

}