int TRIGGER_PIN=23;
int ECHO_PIN=22;
const float SPEED_OF_SOUND=343.0;
void setup()
{
Serial.begin(9600);
pinMode(TRIGGER_PIN, OUTPUT);
pinMode(ECHO_PIN, INPUT);
}
void loop()
{
  digitalWrite(TRIGGER_PIN, LOW);
  delayMicroseconds(2);
  digitalWrite(TRIGGER_PIN, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIGGER_PIN, LOW);
  long duration=pulseIn(ECHO_PIN,HIGH);
  float distance=(duration*0.5*SPEED_OF_SOUND)/10000.0;
  Serial.print("distance:");
  Serial.print(distance,2);
  Serial.println("cm");
  delay(100);
}