Simple Arduino Serial Communication with Echo of line

SerialEchoLine.ino

/**
 * Author: Domenico Monaco
 *
 * Description: Simple Arduino Serial communication, with echo of entire line received. 
 *
 * Source: https://gist.github.com/kiuz/d59519e0de7677df42c3/
 *  
 * License: GNU v2 2014
 */

int incomingByte = 0;    // for incoming serial data

bool waiting = false;

String line = "";

void setup() {
    Serial.begin(9600);
}

void loop() {

  if (Serial.available() > 0) {

    waiting = false; // Set to false, Arduino not in "Waiting" state but are in "Reading" state
    
    incomingByte = Serial.read(); // read Char
    line = line + (char)incomingByte; // add Char to line
    
    delay(1); //Delay of Serial transfer speed
  }else{
    
    //waiting is False only after "reading" state
    //with this line are printed only one times into "waiting" state
    if(waiting==false){
      waiting = true;
      
      // print entire line
      Serial.print(line);
      Serial.print(" ");

      line = ""; // Resete line
      
      Serial.println("");
      Serial.println("Waiting for a message...");
      Serial.println("");}
    }
}