void setup() {
  // put your setup code here, to run once:
  #define trigPin 7
  #define echoPin 6
  #define GREEN_LED 8
  #define YELLOW_LED 12
  #define RED_LED 13

  Serial.begin(9600);
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
  pinMode(GREEN_LED, OUTPUT);
  pinMode(YELLOW_LED, OUTPUT);
  pinMode(RED_LED, OUTPUT);
}

void loop() {
  // put your main code here, to run repeatedly:
  long time;
  long distance;
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);

  time = pulseIn(echoPin, HIGH);
  distance = 0.0343 * (time/2);

  if (distance > 100)
  {
  digitalWrite(GREEN_LED, HIGH);
  digitalWrite(YELLOW_LED, LOW);
  digitalWrite(RED_LED, LOW);
  }
  else if (distance >= 50 && distance <= 100)
  {
  digitalWrite(GREEN_LED, LOW);
  digitalWrite(YELLOW_LED, HIGH);
  digitalWrite(RED_LED, LOW);
  }
  else
  {
  digitalWrite(GREEN_LED, LOW);
  digitalWrite(YELLOW_LED, LOW);
  digitalWrite(RED_LED, HIGH);
  }

  Serial.print("distance: ");
  Serial.print(distance);
  Serial.println("cm");
  delay(200);

}