Arduino Intro: Running LED Lights

Arduino sketch: //running lights using 4 LEDs int pin9=9, pin10=10, pin11=11, pin12=12; void setup() { pinMode(pin9,OUTPUT); pinMode(pin10,OUTPUT); pinMode(pin11,OUTPUT); pinMode(pin12,OUTPUT); } void loop() { digitalWrite(pin12,LOW); digitalWrite(pin9,HIGH); delay(500); digitalWrite(pin9,LOW); digitalWrite(pin10,HIGH); delay(500);