I found out this trick a year and a half too late but here’s how to open, view and edit 2 or more source codes from different directories in the same window using VIM on a mac.
1) esc + :
2) type “vsp” + filepath/filename
e.g. my other C++ source file is in the directory above the one I’m in now, so in my terminal after step 1, I would type ../FirstSolution.cpp then hit enter
vsp means vertical split screen. If you want, type sp for horizontal split screen.
Easy! Although I much prefer sublime text in general, but I know there are some VIM fans out there:)