Andrey Stolyarov (lecturer of the Moscow State University) created a catalog of examples of using the FLTK library for teaching students in the course "Programming: Introduction to the profession":

http://www.stolyarov.info/books/extra/progintro_e2_examples.tgz

10 source files for C ++ examples are in the fltk subdirectory of the archive.
The examples "fonts", "options" and "resize" I liked the most.

The catalog of examples is an addition to the three volumes of the freely available textbook in Russian:

http://www.stolyarov.info/books/programming_intro/e2

    Neato.. I looked over the tar file and there's some nice source code programming examples.
    Under the FLTK directory I tried the fonts FLTK app, and it worked fine.

    I also liked the assembly example programs, like how to copy a file using assembly
    for both linux + freebsd.  Shows the subtle differences in making kernel function calls
    directly without the C library interface.