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

void setup() {
  pinMode(LED_PINS[0], OUTPUT);
  pinMode(LED_PINS[1], OUTPUT);
  pinMode(LED_PINS[2], OUTPUT);
  pinMode(LED_PINS[3], OUTPUT);
  pinMode(LED_PINS[4], OUTPUT);
  pinMode(LED_PINS[5], OUTPUT);
  pinMode(LED_PINS[6], OUTPUT);
  pinMode(LED_PINS[7], OUTPUT);
}

void loop() {
  digitalWrite(LED_PINS[0], HIGH);
  delay(100);
  digitalWrite(LED_PINS[0], LOW);
  
  digitalWrite(LED_PINS[1], HIGH);
  delay(100);
  digitalWrite(LED_PINS[1], LOW);
  
  digitalWrite(LED_PINS[2], HIGH);
  delay(100);
  digitalWrite(LED_PINS[2], LOW);
  
  digitalWrite(LED_PINS[3], HIGH);
  delay(100);
  digitalWrite(LED_PINS[3], LOW);
  
  digitalWrite(LED_PINS[4], HIGH);
  delay(100);
  digitalWrite(LED_PINS[4], LOW);
  
  digitalWrite(LED_PINS[5], HIGH);
  delay(100);
  digitalWrite(LED_PINS[5], LOW);

   digitalWrite(LED_PINS[6], HIGH);
  delay(100);
  digitalWrite(LED_PINS[6], LOW);
  
  digitalWrite(LED_PINS[7], HIGH);
  delay(100);
  digitalWrite(LED_PINS[7], LOW);
}