int pinsCount=3;
int pins[4]={4,8,12};
void setup() {
  // put your setup code here, to run once:
  for (int i=0; i<pinsCount; i++){
    pinMode(pins[i], OUTPUT);
  }
}
void loop() {
  // put your main code here, to run repeatedly:
  for (int i=0; i<pinsCount; i++){
    digitalWrite(pins[i], HIGH);
    delay(100);
    digitalWrite(pins[i], LOW);
    delay(100);
  }
}