int ledBar[] = {27, 26, 22, 21, 20, 19, 18, 17, 16, 15};

void setup() {
  for(int i = 0 ; i < 10 ; i++){
    pinMode(ledBar[i], OUTPUT);
  }
}

void loop() {
  for(int i = 0 ; i < 10 ; i++){
    digitalWrite(ledBar[i], HIGH);
    delay(500);
  }
   for(int i = 9 ; i >= 0 ; i--){
    digitalWrite(ledBar[i], LOW);
    delay(500);
  }
  delay(1); // this speeds up the simulation
}