#define BUTTON_PIN 2
#define LED_PIN 4


void setup() {
  pinMode(LED_PIN, OUTPUT);
  pinMode(BUTTON_PIN, INPUT_PULLUP);
}

void loop() {
  int button_state=digitalRead(BUTTON_PIN);
  if(button_state==LOW)
  {
    digitalWrite(LED_PIN, HIGH);
  }
  else
  {
    digitalWrite(LED_PIN, LOW);
  }
}