CC Mode 5.35 should work out of the box with Emacs >= 24.5. It has been tested on Emacs 24.5, 25.3, 26.3, and 27.1. It may well work on earlier versions, and will likely work on later versions, too. It has also been tested on XEmacs (see below).

If you want to use CC Mode on XEmacs, please download a recent repository head of XEmacs, at least version 7190:2bbae1af16ac from Wed Nov 25 19:09:07 2020 +0000, obtainable from https://foss.heptapod.net/xemacs/xemacs via mercurial. You will also need at least some packages, obtainable from https://foss.heptapod.net/xemacs/xemacs-packages. Build XEmacs and its packages to work together with eachother. Alternatively, any XEmacs release from 2021 onwards should also work.