#include <NewPing.h>
int Total;
const byte numReadings = 20;
byte index;
int Readings[numReadings];
int Smoothed;
#define TRIGGER_PIN  9
#define ECHO_PIN     10
#define MAX_DISTANCE 400 
NewPing sonar(TRIGGER_PIN, ECHO_PIN, MAX_DISTANCE);

void setup(){
Serial.begin(9600);
}
void loop(){
  float Ureadings = sonar.ping_cm();

Total -= Readings[index];
Readings[index] = Ureadings;
Total += Readings[index];
index += 1;

if (index >= numReadings)

{
 index = 0;
}

Smoothed = Total/numReadings;

  Serial.print("Distance: ");
  Serial.print(Smoothed);
  Serial.println("cm");
}