const int LEDpin [] = {3,5,6,9,10};
const int numLED = sizeof(LEDpin) / sizeof(LEDpin[0]);
void setup() {
for (int i = 0 ; i < numLED ; i ++) {
  pinMode(LEDpin[i] , OUTPUT);
}
}

void loop() {
for (int i = 0 ; i < numLED ; i ++) {
  digitalWrite(LEDpin[i] , HIGH);
    delay(500);
}
for (int i = 0 ; i < numLED ; i ++) {
  digitalWrite(LEDpin[i] , LOW);
    delay(500);
}
}