void setup ()
{
  pinMode (A0, INPUT);
  pinMode (7, OUTPUT);
  Serial.begin(9600);
}


void loop ()
{
 int ldrvalue = analogRead(A0);
  Serial.println(ldrvalue);
  if (ldrvalue > 500)
  {
    digitalWrite(7,HIGH);
    tone (3, 399, 350);
    delay (50);
  }
  else
  {
    digitalWrite(7, LOW);
    noTone(3);
    delay(50);
  }
}