int pin;
void setup(){
for(pin=12;pin<=19;pin++)
{
pinMode(pin, OUTPUT);

  }
}

void loop() 
{
for(pin=12;pin<=19;pin++)
{
digitalWrite(pin, HIGH);
delay(20);
digitalWrite(pin, LOW);
delay(30);
}
for(pin=19;pin>=12;pin--)
{
digitalWrite(pin, HIGH);
delay(20);
digitalWrite(pin, LOW);
delay(30);
}

 
}