bool zeromsg_Printed = false;

void setup() {
  // put your setup code here, to run once:
Serial.begin(9600);
}

void loop() {
  // put your main code here, to run repeatedly:
    int incomming_Msg_size;
    if (Serial.available() > 0)
    {
      delay(20); // Wait 20ms for the rest of the characters to arrive
      incomming_Msg_size = Serial.available();
      Serial.print("incomming_Msg_size : ");
      Serial.println(incomming_Msg_size);

      while(Serial.available() > 0){   // to delete incomming data
        Serial.read();                 // to delete incomming data

        zeromsg_Printed = false;

      }

    }
    else {

        incomming_Msg_size = Serial.available();

        if (!zeromsg_Printed)
        {
          Serial.print("No incomming_Msg_size : ");
          Serial.println(incomming_Msg_size);
          zeromsg_Printed = true;
        }

    }


}