In the old ages when I was taught Pascal, the manual had nice
syntax diagrams. Each grammatical structure was shown as
round boxes connected by arrows, with a model railway look,
with the boxes representing either lexical tokens or other
diagrams (i.e. terminals/nonterminals). They seemed very
intuitive because you could toot-toot one finger along the
rails in the book while moving another finger over your code.

Does anything similar exist for C++? Or am I stuck with the bnf?
(I really appreciate the hyperlinked version http://www.nongnu.org/hcb/
but it's still a mess...)

If I have to create the diagrams myself, I might as well use UML,
that being the company standard. But I'm not sure whether I
shold use state diagrams or activity diagrams or something else
- the state diagrams are conceptually close but they represent
states as boxes and transitions as arrows, which is the opposite
of what I want. Activity diagrams seem a better graphical match
but perhaps less appropriate conceptually.

Any hints?