Because I also write fiction as a hobby, I researched this kind of question once. The only law I had available was USA Copyright Law. Staring in 1974, copyright is in place, whether or not it was registered, the moment that you mark the documents, modules, etc. However, you must follow certain rules.
If the work to be copyrighted exists as a single file, one set of marks is enough. You must have the year, the copyright symbol (but parenthesis -small c - parenthesis is acceptable), and the name of the work's owner. To preserve international copyright rights, you must include the phrase "All Rights Reserved."
When it becomes a multiple-file program, the requirements I mentioned above apply to each file. It is permitted but not required to identify a file as part of a larger work.
You can find on-line help easily enough to get the fine points handled, so I won't go into them. However, one issue that MUST be considered is that if your work is a program that actively does something, it is required that the date, copyright symbol (c), and owner's name must appear in some sort of display image that is one of the first outputs of the program. For instance, put up a "splash graphic" for the first couple of seconds after the program starts. Include the copyright notice in the splash.