#include  <Servo.h>
Servo myservo;
int pos = 0;

void setup() {
   myservo.attach(12);
  // put your setup code here, to run once: 

}

void loop() {
  for (pos =0 ,pos <=180, pos += 1) { //goes from 0 degrees to 180 degrees 
  // in step of 1 degree}
  myservo.write(pos); // tell servo to change position of variable'pos'
  delay(15); // wait 15ms for servo to reach position
  }
  for (pos =180,pos>=0, pos -= 1){ //goes from 180 degrees to 0 derees
  //in step of 1 degree}
  myservo.write(pos);//to servo to change position of variable 'pos'
  delay(15);//wait 15ms for servo to reach position
  // put your main code here, to run repeatedly:
  }
}