int LED = 8;
int PB = 7;

void setup() {
  // put your setup code here, to run once:
  pinMode(LED, OUTPUT);
  pinMode(PB, INPUT_PULLUP);
}

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