arduino - very basic state-machine

int idx = 1;

void timed_action() {
  switch(idx){
    case 1: //turn on one led
      idx++;
      break;
    case 2: //turn on two leds
      idx++;
      break;
    case 3: //turn on three leds
      idx++;
      break;
    case 4: //turn on four leds
      idx++;
      break;
    case 5: //no changes
      break;
  }
}