int cm = 0;

const int triggerPin = 7;
const int echoPin = 7;

const int redLED = 6;
const int yellowLED = 2;
const int greenLED = 4;

long readUltrasonicDistance(int triggerPin, int echoPin) {
  pinMode(triggerPin, OUTPUT);
  digitalWrite(triggerPin, LOW);
  delayMicroseconds(2);
  digitalWrite(triggerPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(triggerPin, LOW);

  pinMode(echoPin, INPUT);
  return pulseIn(echoPin, HIGH);
}

void setup() {
  Serial.begin(9600);

  pinMode(redLED, OUTPUT);
  pinMode(yellowLED, OUTPUT);
  pinMode(greenLED, OUTPUT);

  digitalWrite(redLED, LOW);
  digitalWrite(yellowLED, LOW);
  digitalWrite(greenLED, LOW);
}

void loop() {
  cm = 0.01723 * readUltrasonicDistance(triggerPin, echoPin);

  Serial.print("Mesafe: ");
  Serial.print(cm);
  Serial.println(" cm");

  digitalWrite(redLED, LOW);
  digitalWrite(yellowLED, LOW);
  digitalWrite(greenLED, LOW);

  if (cm > 0 && cm < 100) {
    digitalWrite(redLED, HIGH);
  } else if (cm >= 100 && cm < 200) {
    digitalWrite(yellowLED, HIGH);
  } else if (cm >= 200 && cm < 300) {
    digitalWrite(greenLED, HIGH);
  }

  delay(500);
}