On Sat, 1 Sep 2018 02:49:26 +0100, Roger Johnson
wrote:

youtube-dl.exe - System Error
The code execution cannot proceed because MSVCR100.dll
was not found. Reinstalling the program may fix this problem.

All I did was download this executable & double click on it to get that!
https://youtube-dl.org/downloads/latest/youtube-dl.exe

What Windows 10 program am I supposed to reinstall and how do I do that?

I had the same problem on some Windows 10 installs.
I solved it by installing vcredist_x86.exe from Microsoft.