#include <Servo.h>
Servo servo; //creat servo object to control a servo
int pos = 0;

void setup() {
  servo.attach(3);
  // put your setup code here, to run once:

}

void loop() {
  for (pos=0;pos<=180;pos+=1) {
  // in step of 1 degree
  servo.write(pos);
  delay(0);  // put your main code here, to run repeatedly:

}
for (pos=180;pos>=0;pos-=1)  {
  servo.write(pos);
  delay(100);
}
}