hc-sr04 distance sensor

Hi all
I am really new in this and try a simple progect. Just to conect a hc-sr04 distance sensor and read the results at Serial monitor.
i am using this sketch
#include <NewPing.h>

#define TRIGGER_PIN 14
#define ECHO_PIN 15
#define MAX_DISTANCE 200

NewPing DistanceSensor(TRIGGER_PIN, ECHO_PIN, MAX_DISTANCE);

void setup()
{
Serial.begin(9600);
}

void loop()
{
unsigned int cm = DistanceSensor.ping_cm();
Serial.print("Distance: ");
Serial.print(cm);
Serial.println(“cm”);
delay(1000);
}
but my serial monitor keeps printing distance 0
can anyone help me with that ?
Thanx in advance

You are not using any of the digital pins, except 0 and 1. So, why use analog pins as digital pins, when there are 11 free digital pins?

Are you sure that you have the trigger pin and echo pins connected to the appropriate pins on the sensor? What are the other two pins connected to?

http://arduinobasics.blogspot.com/2012/11/arduinobasics-hc-sr04-ultrasonic-sensor.html