int led_pin = 4;
int ldr_pin = A0;
int data;
int ldr_value;
int threeshold = 500;
void setup() {
  pinMode(led_pin, OUTPUT);
 Serial.begin(9600);

}

void loop() {
 if (Serial.available()> 0) {
  data = Serial.read();
  Serial.println(data);

  if (data != 0) {
    threeshold = data;
  }
 }

 ldr_value = analogRead(ldr_pin);

 if (ldr_value > threeshold) {
  digitalWrite(led_pin, HIGH);
 }
 else {
  digitalWrite(led_pin, LOW);
 }

 Serial.print("data = ");
 Serial.print(data);
 Serial.print("\t");
 Serial.print("threeshold = ");
 Serial.print(threeshold);
 Serial.print("\t");
 Serial.print("ldr value = ");
 Serial.print(ldr_value);
 Serial.print("\n");
}