int button = 4;
int led = 3;
bool button_val = 0;

void setup() {
  pinMode(led, OUTPUT);
  pinMode(button, INPUT);
}

void loop() {
  button_val = digitalRead(button);

  if (button_val == 1) {
  digitalWrite(led, HIGH);
  } else {
    digitalWrite(led, LOW);
  }
}