const int ledpin = 13;
const int ldrpin = A0;
void setup(){
  Serial.begin(9600);
  pinMode(ledpin, OUTPUT);
  pinMode(ledpin, INPUT);
}
void loop(){
  int ldr = analogRead(ldrpin);
  if (ldr<500){
  digitalWrite(ledpin, HIGH);
  Serial.print("its night time,turn on led:");
  Serial.println(ldr);  
}
else{
  digitalWrite(ledpin, LOW);
  Serial.print("its day time,turn off led:");
  Serial.println(ldr);  
}
delay(2000);
}