The LaTeX source code has definitions for the constants \@ne, \tw@, \thr@@. It's a microoptimization that is useful because of the way the TeX/LaTeX parsers work. I don't understand the details, it's beyond my LaTeX wizardry. http://tex.stackexchange.com/questions/9787/ne-tw-thr

On the other hand, I think that this kind of definitions are not useful for C.