Servo motor + ultrasonic sensor

#include<Servo.h>
int trig=8;
int echo=9;
int dt=10;
Servo servo;

//int distance,duration;
void setup() {
  // put your setup code here, to run once:
pinMode(trig,OUTPUT);
pinMode(echo,INPUT);
Serial.begin(9600);
servo.attach(11);
}

void loop() {
  // put your main code here, to run repeatedly:


if (calc_dis()<10)
{
  for (int i=0;i<=540;i++)
  {
    servo.write(i);
    delay(1);
  }
  delay(100);
  for (int i=540;i>=0;i--)
  {
    servo.write(i);
    delay(1);
  }
  delay(100);
}
}

//This code is written to calculate the DISTANCE using ULTRASONIC SENSOR

int calc_dis()
{
  int duration,distance;
  digitalWrite(trig,HIGH);
  delay(dt);
  digitalWrite(trig,LOW);
  duration=pulseIn(echo,HIGH);
  distance = (duration/2) / 29.1;
  return distance;
}