int led1Pin = 4;
int led2Pin = 5;
void setup() {
  // we will use two pins for two LEDs
  pinMode(led1Pin, OUTPUT);
  pinMode(led2Pin, OUTPUT);
}

void loop() {
  // put your main code here, to run repeatedly:
  setPin1(HIGH); 
  setPin1(LOW);

}
void setPin1(int led1){
  digitalWrite(led1Pin, led1); //set pin 4 to output LOW or HIGH voltage

  if(led1 == HIGH){
   digitalWrite(led2Pin, LOW); // if pin 4 is outputting HIGH voltage, pin 5 should output LOW
  }else{
    digitalWrite(led2Pin, HIGH); // otherwise pin 5 should output HIGH 
  }
  
  delay(1000); // delay of 1000 ms
}