#define LED1_PIN 9
#define LED2_PIN 10
#define LED3_PIN 11
#define LED4_PIN 12

const int NUM_LEDS = 4;
const int ledPins[NUM_LEDS] = {LED1_PIN, LED2_PIN, LED3_PIN, LED4_PIN};

const int INTERVAL = 200;

void setup() {
  for (int i = 0; i < NUM_LEDS; i++) {
    pinMode(ledPins[i], OUTPUT);
    digitalWrite(ledPins[i], LOW);  
  }
}

void loop() {
  for (int i = 0; i < NUM_LEDS; i++) {
    digitalWrite(ledPins[i], HIGH);  
    delay(INTERVAL);                  
    digitalWrite(ledPins[i], LOW);   
  }
}