const int TrigPin = 4;
const int EchoPin = 2;
const int RLED = 7;
const int GLED = 8;

long duration;
int distance;

void setup()
{
  Serial.begin(9600);
  pinMode(TrigPin, OUTPUT);
  pinMode(EchoPin, INPUT);
  pinMode(RLED, OUTPUT);
  pinMode(GLED, OUTPUT);
}

void loop()
{
  digitalWrite(TrigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(TrigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(TrigPin, LOW);

  duration = pulseIn(EchoPin, HIGH);
  distance = duration * 0.034 / 2;

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

  if (distance < 100) {
    digitalWrite(RLED, HIGH);
    digitalWrite(GLED, LOW);
  } else {
    digitalWrite(RLED, LOW);
    digitalWrite(GLED, HIGH);
  }

  delay(200);
}