#include<Servo.h>
Servo servo1;
int i;
void setup() //code which execute only once
{
Serial.begin(9600);
servo.attach(9);
servo.write(0);
}
void loop() //code which execute repeatedly in loop 
{
for(i=1; i<=180; i=i+1) 
{
servo1.write (i);
delay(10);
}
for(i=180; i>=1; i=i-1) 
{
servo.write(i);
delay(10);
}
}