Print to serial only once in loop

Projects Programming
2

Start by getting rid of the delay(50). That's going to mess up anything else that you might want to do with this code in the future.

void loop() {
  static unsigned long lastPrinted;
  const unsigned long printInterval = 50; //milliseconds, how often to print
  if(millis() - lastPrinted >= printInterval) {
    printLowPins();
    lastPrinted = millis();
  }
  //any other code can go here and it gets run very rapidly
}

Now we can take your code above and put it into the printLowPins() function I just imagined. You said that you always want it to print something, just a single 'S' if there's no pins low at all?

void printLowPins() {
  bool nothingPrinted= true;
  for(int i = 0; i <= 10; i++){
    if (digitalRead(i) != true){
      Serial.println(i);
      nothingPrinted= false;
    }
  }
  if(nothingPrinted) {
    Serial.println("S");
  }
}

Note: you may want to change .println() to .print() to put it on one line like your example.