void setup() {
      Serial.begin(9600);
      while (!Serial) {
        ;  // wait for serial port to connect. Needed for native USB port only
      }
      int x = 42;
      Serial.print("The absolute value of ");
      Serial.print(x);
      Serial.print(" is ");
      Serial.println(abs(x));
      x = -42;
      Serial.print("The absolute value of ");
      Serial.print(x);
      Serial.print(" is ");
      Serial.println(abs(x));
    }

    void loop() {
    }