#include <Servo.h>

Servo servo; // create servo object to control a servo 

int pos = 0;  // variable to store the servo position

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

void loop(){
 for (pos=0;pos<=180;pos+i=1) {//rotate from 0 degrees to 180 degrees
   //in steps of 1 degree 
servo.write(pos);        //tell servo to go to  the position in variable 'pos
   delay(10);           //waits 10ms for the servo to reach the position
 }

  for (pos=180;pos>=0;pos-=1){//rotatefrom 180 degrees to 0 degrees}
  servo.write(pos);        //waits 10ms for the servo to reach the position
  }
}