Have you actually tried to get YouCompleteMe[1] to work for C/C++ autocomplete? It's a huge PIA. Autocomplete just works in VSCode and many other IDEs once you point them at the right directory.
The one problem I had was that I had to use the system version of clang as I'm using Arch.
That said, there is a fair bit of built-in auto completion in vanilla vim (on par with VSC), and a few quick rebinds might be all you need. I would suggest checking it out.
:help 24.3
Frankly, I would use neovim + deoplete. Modern, async, and a big user community right now (almost everyone with neovim runs deoplete).
[0] https://github.com/zchee/deoplete-clang [1] https://github.com/zchee/deoplete-clang/issues/57
./install.py --clang-completer --gocode-completer --racer-completer