const int ledPin = 2;       
const int buttonPin = 4;    

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

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

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