#define trigPin 7
#define echoPin 8
 long duration;
  long distance;
int numberOfSamples = 10, counter=0;
long sum=0; 

void setup()
{
  pinMode(trigPin, OUTPUT);
   pinMode(echoPin, INPUT);
  Serial.begin(9600);
}

void loop()
{
  while(counter <numberOfSamples){
    
  getDistance();
    
    if(distance>3 && distance <300){
    sum+=distance;
      counter++;
    }
  }
    
  Serial.print("average distance[cm] = ");
  Serial.println(sum*1.0/counter);
  delay(10);
  counter = 0;
  sum=0;
}

void getDistance(){
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2); 
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);
  
  duration = pulseIn(echoPin,HIGH);
  distance = duration/58.1;
  
}