void setup()
{
pinMode(2,OUTPUT); //sets the number 0 digital pin of the Arduino in output mode
pinMode(1,OUTPUT); //sets the number 1 digital pin of the Arduino in output mode
}
 
void loop(){
digitalWrite(2,HIGH); //red LED lights up
digitalWrite(1,LOW); //green LED goes out
delay(2000);
digitalWrite(2,LOW); //red LED goes out
digitalWrite(1,HIGH); //green LED lights up
delay(2000);
}