Arduino Uno with ULTRASONIC SENSOR

/*
* Ultrasonic Sensor HC-SR04 and Arduino Tutorial
*
* Builded by Teodor Hristov
* www.dev-hn.com
*
*/

// defines pins numbers
int trig = 2;
int echo = 3;
int go = 4;

// defines variables
long duration;
int distance;

void setup() {
pinMode(go, OUTPUT);
pinMode(trig, OUTPUT); // Sets the trig as an Output
pinMode(echo, INPUT); // Sets the echo as an Input
Serial.begin(9600); // Starts the serial communication
}

void loop() {
// Clears the trig
digitalWrite(trig, LOW);
delayMicroseconds(2);

// Sets the trig on HIGH state for 10 micro seconds
digitalWrite(trig, HIGH);
delayMicroseconds(10);
digitalWrite(trig, LOW);

// Reads the echo, returns the sound wave travel time in microseconds
duration = pulseIn(echo, HIGH);

// Calculating the distance
distance= duration*0.034/2;

if (distance > 50){

 digitalWrite(go, HIGH);// High voltage on go or pin 4
  }
  else {
    digitalWrite(go, LOW);

    }


// Prints the distance on the Serial Monitor
Serial.print("Distance: ");
Serial.println(distance);
delay(250); //1/4 from 1 sec
}