Serial Communication String LED On Off

reference website: http://www.chrisbrand.co.za/2013/06/30/arduino-serial-port/



 /*
   Simple LED sketch
   */
 
  int led = 13; // Pin 13
 
  void setup()
  {
      pinMode(led, OUTPUT); // Set pin 13 as digital out

     // Start up serial connection
     Serial.begin(9600); // baud rate
     Serial.flush();
 }

 void loop()
 {
     String input = "";

     // Read any serial input
     while (Serial.available() > 0)
     {
         input += (char) Serial.read(); // Read in one char at a time
         delay(5); // Delay for 5 ms so the next char has time to be received
     }

     if (input == "on")
     {
         digitalWrite(led, HIGH); // on
     }
     else if (input == "off")
     {
         digitalWrite(led, LOW); // off
     }
 }