const int ledPin = 13;
const int sensorPin = 3;

int val;

void setup() {
   pinMode(ledPin, OUTPUT);
   pinMode(sensorPin, INPUT);
}

void loop() {
   // check the state of the button
   val = digitalRead(sensorPin);
   if (val == HIGH) {
      digitalWrite(ledPin, HIGH);
   } else {
      digitalWrite(ledPin, LOW);
   }
}