int led = 5;
int btn = 7;

void setup() {
  // put your setup code here, to run once:
  pinMode(led, OUTPUT);
  pinMode(btn, INPUT_PULLUP);
  digitalWrite(led, LOW); 
}

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