But now it's working in Serial Monitor. What will be if i want connect tho boards and send long strings from one to second??? It will be working without checking "new line symbol"???
If you want to send 'messages' instead of 'characters' you need a way for the receiving system to recognize when it has received the end of the 'message'. You can use '\n' or some other character that is not going to be part of your message. Even if your messages are fixed in length (always the same number of characters) it is good to add special characters before and after the message to protect against data loss or data inserted due to noise.