int echoPin = 3, trigPin = 5, gLed = 6, rLed = 7, buzzer = 8;
void setup() {
  pinMode(echoPin, INPUT);
  pinMode(trigPin, OUTPUT);
  pinMode(gLed, OUTPUT);
  pinMode(rLed, OUTPUT);
  pinMode(buzzer, OUTPUT);
  digitalWrite(gLed, LOW);
  digitalWrite(rLed, LOW);
  digitalWrite(buzzer, LOW);
}

void loop() {
  long duration, distance;
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);
  duration = pulseIn(echoPin, HIGH);
  distance = (duration/2)/29.1;
  if(distance <= 200 && distance >=100)
  {
    digitalWrite(gLed, HIGH);
    delay(500);
    digitalWrite(gLed, LOW);
  }
  else if(distance < 100 && distance >= 30)
  {
    digitalWrite(buzzer, HIGH);
    delay(100);
    digitalWrite(rLed, HIGH);
    delay(500);
    digitalWrite(rLed, LOW);
  }
}