int trigpin = 18;
int echopin = 16;
float distance, duration;

void setup() {
  Serial.begin(115200);
  pinMode(trigpin, OUTPUT);
  pinMode(echopin, INPUT);
}

void loop() {
  digitalWrite(trigpin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigpin, LOW);
  duration = pulseIn(echopin, HIGH);
  distance = 0.017 * duration;

  if(distance <= 10){
    tone(32, 500);
  }else if(distance > 10 && distance <= 20 ){
    tone(32, 1250);
  }else{
    tone(32, 0);
  }

  Serial.print("Distance = ");
  Serial.print(distance);
  Serial.println("cm");
  delay(1000);
}