int lampa=9;
int knopka=2;

void setup() {
  // put your setup code here, to run once:
  pinMode(lampa, OUTPUT);
  pinMode(knopka, INPUT);
}

void loop() {
  // put your main code here, to run repeatedly:
  if(digitalRead(knopka)==LOW){
    digitalWrite(lampa, LOW);
  }
  else{
    digitalWrite(lampa, HIGH);
  }
}