int LED=4;
int SW=2;
void setup() {
  pinMode(LED, OUTPUT);//LED OUTPUT
  pinMode(SW, INPUT);//SW INPUT
}
void loop()
 {
  if(digitalRead(SW)==LOW){
    digitalWrite(LED,HIGH);   // turn the LED on (HIGH is the voltage level)
  }
 else{
   digitalWrite(LED,LOW);    // turn the LED off by making the voltage LOW
     }
 }