const int ledPins[4] = {10, 11, 12, 13};

void setup() {
  for(int i = 0; i < 4; i++) {
    pinMode(ledPins[i], OUTPUT);
  }
}

void loop() {
  for(int i = 0; i < 4; i++) {
    digitalWrite(ledPins[i], HIGH);
    delay(1000);
    digitalWrite(ledPins[i], LOW);
    delay(1000);
  }
}