const int NUM_LEDS = 9;
const int LED_PINS[NUM_LEDS] = {13, 12, 11, 10, 9, 8, 7, 6, 5};
const int BTN_PIN = 4;

int count = 0;
int oldBtnState = HIGH;

void checkButton()  {
  int btnState = digitalRead(BTN_PIN);
  if (oldBtnState != btnState)  {
    oldBtnState = btnState;
    if (btnState == LOW)  {
      Serial.println("Button pressed");
      count++;
      if (count == NUM_LEDS + 1) {
        count = 0;
        // turn all LEDs off
        for (int i = 0; i <= NUM_LEDS; i++)  {
          digitalWrite(LED_PINS[i], LOW);
        }
      }
    } else {
      Serial.println("Button released");
    }
    delay(20);  // debounce
  }
}

void setup() {
  Serial.begin(115200);
  for (int i = 0; i < NUM_LEDS; i++)  {
    pinMode(LED_PINS[i], OUTPUT);
  }
  pinMode(BTN_PIN, INPUT_PULLUP);
}

void loop() {
  checkButton();
  if (count > 0)  {
    digitalWrite(LED_PINS[count - 1], HIGH);
  }
}