State button and flashing led

button_flash_led.ino

const int LED_PIN = 3;
const int BTN_PIN = 4;
const int FLASH_MILLIS = 100;

void setup() {

  pinMode(LED_PIN, OUTPUT);
  pinMode(BTN_PIN, INPUT);
}

bool button_state = false;
bool led_flash = false;
bool led_state = false;
int last_change = 0;

void loop() {

  int now = millis();

  if (digitalRead(BTN_PIN) == HIGH ^ button_state)
  {
    button_state = !button_state;
    if (button_state)
    {
      led_flash = !led_flash;
      delay(100);
    }
  }

  if (led_flash || led_state)
  {
    if (now - last_change > FLASH_MILLIS)
    {
      led_state = !led_state;
      digitalWrite(LED_PIN, led_state ? HIGH : LOW);
      last_change = now;
    }
  }


}