Is there actually a Da Vinci code?

Like why would Dan Brown write a book with more than 80 chapters just to tell us some fiction story, like if the Da Vinci code is so useless, why did they make a hole movie about it? is there an actual code? like in the book you read Robert Langdon discovering a death man and studying him , like when is their talked about cracking the code, was the code just a stupid one made up by the death guy just to tell them how he died; stupid me, i actually thought there was a real difficult code of Da Vinci himself that needed to be cracked, i found the book a bit of a disappointment actually, like what is the meaning of this book, it hadn't to do anything with da vinci himself, its more like a police story.. any comments?