Copy-paste of entire program:

#if (ARDUINO >= 100)
  #include <Arduino.h>
#else
  #include <WProgram.h>
#endif

#include <avr/io.h>
#include <avr/interrupt.h>
#include <math.h>
#include <ros.h>
#include <std_msgs/Int64.h>
#include <std_msgs/UInt16.h>
#include <std_msgs/Float32.h>
#include <simple_arm/GoToPosition.h>

#define PWM 5
#define CW 7
#define CCW 8
#define encoderPinA 2
#define encoderPinB 3
#define lim_sw 10

ros:: NodeHandle nh;

float count;

float des_angle, act_angle, diff_error, int_error, motorVolt;
float Kp, Ki, Kd, error, prverror, myBit, de, dt, sum_error;
float nowtime, prvtime;

void encoder_cb( const std_msgs::UInt16& cmd_msg){

  nowtime = millis()/1000.0;

  de = error - prverror;
  dt = nowtime - prvtime;
  sum_error = error+prverror;

  Kp = 0.02; 
  Ki = 0.5; //Gains
  Kd = 1.5;

  des_angle =  cmd_msg.data; 
  act_angle = (360.0/3266.5) * count;


  error = des_angle - act_angle;
  diff_error = de/dt;
  int_error = sum_error*dt;

  motorVolt = (Kp*(error))+(Kd*(diff_error))+(Ki*(int_error));

  myBit = (abs(motorVolt)/12.0)*255;
  myBit = constrain (myBit,0,255);

  if (des_angle > act_angle)
  {
    digitalWrite(CW,HIGH);
    digitalWrite(CCW,LOW);
  }
  else if ( des_angle < act_angle )
  {
    digitalWrite(CW,LOW);
    digitalWrite(CCW,HIGH);
  }

  analogWrite(PWM,myBit);

  prverror = error;
  prvtime = nowtime;

}

ros::Subscriber<std_msgs::UInt16> sub("servo", encoder_cb);

void setup() {

  pinMode(PWM,OUTPUT);
  pinMode(CW,OUTPUT);
  pinMode(CCW,OUTPUT);
  pinMode(encoderPinA,INPUT);
  pinMode(encoderPinB,INPUT);
  attachInterrupt(digitalPinToInterrupt(2), readEncoder ,CHANGE);
  Serial.begin(57600);
  digitalWrite(lim_sw,HIGH);
  nh.initNode();
  nh.subscribe(sub);
}

void readEncoder()
{
  if(digitalRead(encoderPinA) == digitalRead(encoderPinB))
  {
    count = count - 1;
  }
  else
  {
    count = count + 1;
  }
}


void loop(){

  nh.spinOnce();

}