#define LDR 2
#define LED 3

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

void loop() {
  // put your main code here, to run repeatedly:
  if(digitalRead(LDR) == 1)
     digitalWrite(LED, HIGH);
     else
     digitalWrite(LED, LOW);
  delay(1); // this speeds up the simulation
}