int ldr= 4;
int led=10;

void setup() {
  // put your setup code here, to run once:
pinMode(ldr, INPUT);
pinMode(led, OUTPUT);
Serial.begin(9600);
}

void loop() {
  // put your main code here, to run repeatedly:
if (digitalRead(ldr)==LOW)
{
  Serial.println("Light");
  digitalWrite(led, LOW);
}
else
{
  Serial.println("Dark");
digitalWrite(led, HIGH);
delay(200);
}
}