const int trigPin = 9;
const int echoPin = 10;
const int redLightPin = 11;
const int yellowLightPin = 12;
const int greenLightPin = 13;

long duration;
int distance;
int pos;

void setup() {
  
  pinMode(trigPin, OUTPUT); 
  pinMode(echoPin, INPUT); 
  pinMode(redLightPin, OUTPUT);
  pinMode(yellowLightPin, OUTPUT);
  pinMode(greenLightPin, OUTPUT);
  
  Serial.begin(9600);

  digitalWrite(redLightPin, LOW);
  digitalWrite(yellowLightPin, LOW);
  digitalWrite(greenLightPin, LOW);
  

}

void loop() {
  
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);

  // Sets the trigPin on HIGH state for 10 micro seconds
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);

  // Reads the echoPin, returns the sound wave travel time in microseconds
  duration = pulseIn(echoPin, HIGH);

  // Calculating the distance
  distance = duration * 0.034 / 2;
  
  if (distance > 100) {
    digitalWrite(redLightPin, LOW);
    digitalWrite(yellowLightPin, LOW);
    digitalWrite(greenLightPin, HIGH);
    
  }

  else if (distance <= 100 && distance >= 50) {
    digitalWrite(redLightPin, LOW);
    digitalWrite(yellowLightPin, HIGH);
    digitalWrite(greenLightPin, LOW);
    
  }

  else {
    digitalWrite(redLightPin, HIGH);
    digitalWrite(yellowLightPin, LOW);
    digitalWrite(greenLightPin, LOW);
    
  }


  // Prints the distance on the Serial Monitor
  Serial.print("Distance: ");
  Serial.println(distance);

}