#define trigPin 9
#define echoPin 10
#define redLED 3
#define greenLED 4

long duration;
int distance;

void setup() {
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
  pinMode(redLED, OUTPUT);
  pinMode(greenLED, OUTPUT);
  Serial.begin(9600);
}

void loop() {
  // Send ultrasonic pulse
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);

  // Read echo response
  duration = pulseIn(echoPin, HIGH);
  distance = duration * 0.034 / 2; // Convert to cm

  Serial.print("Distance: ");
  Serial.print(distance);
  Serial.println(" cm");

  // Check if parking slot is occupied or free
  if (distance < 50) {
    digitalWrite(redLED, HIGH);    // Slot occupied
    digitalWrite(greenLED, LOW);
  } else {
    digitalWrite(redLED, LOW);     // Slot free
    digitalWrite(greenLED, HIGH);
  }

  delay(500);
}