int ldr_A0_pin = A3;
int ldr_A0_val;

int ldr_D0_pin = 4;
int ldr_D0_val;

void setup() {
  pinMode(ldr_D0_pin, INPUT);
  Serial.begin(9600);
}

void loop() {
  // using ldr as analog
  // ldr_A0_val = analogRead(ldr_A0_pin);
  // Serial.println(ldr_A0_val);

  // using ldr as digital
  ldr_D0_val = digitalRead(ldr_D0_pin);
  Serial.println(ldr_D0_val);

}