int led_pin = 12;
int button_pin = 2;

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

void loop() {
  // put your main code here, to run repeatedly:
  if (digitalRead(button_pin) == LOW) {   // button not pressed
    digitalWrite(led_pin, LOW);           // led is low
  } else {
    digitalWrite(led_pin, HIGH);
  }
}