#include <Servo.h>

Servo myservo;  

int angle = 0;    // variable to store the servo angle

void setup() {
  myservo.attach(9);  // attaches the servo on pin 9 to the servo object
}

void loop() {
  for (angle = 0; angle <= 180; angle += 1) { // goes from 0 degrees to 180 degrees
    // in steps of 1 degree
    myservo.write(angle);              // tell servo to go to position in variable 'pos'
    delay(15);                       // waits 15ms for the servo to reach the position
  }
  for (angle = 180; angle >= 0; angle -= 1) { // goes from 180 degrees to 0 degrees
    myservo.write(angle);              // tell servo to go to position in variable 'pos'
    delay(15);                       // waits 15ms for the servo to reach the position
  }
}