int trigger = 3;
int echo = 2;
 
void setup() {
Serial.begin(9600);
}
 
void loop()
{

long duration, inches, cm;
 
pinMode(trigger, OUTPUT);
digitalWrite(trigger, LOW);
delayMicroseconds(2);
digitalWrite(trigger, HIGH);
delayMicroseconds(10);
digitalWrite(trigger, LOW);

pinMode(echo, INPUT);
duration = pulseIn(echo, HIGH);
 
inches = microsecondsToInches(duration);
cm = microsecondsToCentimeters(duration);
 
Serial.println(cm, DEC);
 
delay(100);
}
 
long microsecondsToInches(long microseconds){

return microseconds / 74 / 2;
}
 
long microsecondsToCentimeters(long microseconds){

return microseconds / 29 / 2;
}