const int buttonPin = 2; 
const int ledPin = 13;    

void setup() {
  pinMode(buttonPin, INPUT_PULLUP);  
  pinMode(ledPin, OUTPUT);          
}

void loop() {
  int buttonState = digitalRead(buttonPin);  

  if (buttonState == LOW) {  
    digitalWrite(ledPin, HIGH);  
  } else {
    digitalWrite(ledPin, LOW);   
  }
}