Using Ultrasonic Sensor

const int trigPin = 2; // Trigger Pin of Ultrasonic Sensor
const int echoPin = 3; // Echo Pin of Ultrasonic Sensor
void setup()
{
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
Serial.begin(9600); // Starting Serial Terminal
}
void loop()
{
long duration, inches, cm;

digitalWrite(trigPin, LOW);
delayMicroseconds(2);
digitalWrite(trigPin, HIGH);
delayMicroseconds(10);
digitalWrite(trigPin, LOW);

duration = pulseIn(echoPin, HIGH);
inches = microsecondsToInches(duration);
cm = microsecondsToCentimeters(duration);
Serial.print(inches);
Serial.print("in, ");
Serial.print(cm);
Serial.print("cm");
Serial.println();
delay(1000);
}
long microsecondsToInches(long microseconds)
{
return microseconds / 74 / 2;
}
long microsecondsToCentimeters(long microseconds)
{
return microseconds / 29 / 2;
}