void setup() {
String string1 = "Hello!";
String string2 = "Arduino.";
String stringSum = "anyvalue";
}
void loop() {
  Serial.begin(9600);
  delay(5000);
  Serial.println("string1");
  Serial.println("string2");
  Serial.println("stringSum");

  Serial.println("#1");
  Serial.print("string1");
  Serial.println("string2"); // Hello!Arduino.

  Serial.println("#2");
  stringSum = string1 + string2;
  Serial.println(stringSum); //Hello!Arduino.

  Serial.println("#3");
  Serial.println(string1 + "Cambodia.");//Hello!Cambodia
}