const int LED_PINS[] = {2, 4, 7, 8};
const int LED_COUNT = sizeof(LED_PINS) / sizeof(LED_PINS[0]);

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

void loop() {
  for (int i = 0; i < LED_COUNT; i++) {
    digitalWrite(LED_PINS[i], HIGH);
    delay(1000);
    digitalWrite(LED_PINS[i], LOW);
    delay(1000);
  }
}