msvcp100.dll
This file belongs to Microsoft Visual C++ 2010 Redistributable. Install that package and the DLL arrives with it, in the right place and correctly registered.
Do not download this DLL on its own
Searching for a missing DLL by name leads to sites that hand you that single file. It is one of the oldest and most effective malware delivery methods there is, and a system DLL from an unknown source is indistinguishable from a deliberately modified one. There is never a legitimate reason to obtain a runtime component that way.
What it is
The C++ standard library from the Visual Studio 2010 runtime, shipping in the same 2010 redistributable as msvcr100.dll.
Where you see it: The same era of software, usually reported alongside msvcr100.dll.
Same answer as msvcr100.dll: the 2010 redistributable from Microsoft directly. Newer Visual C++ packages do not replace it.
We do not index this package
We have no verified download to give you for Microsoft Visual C++ 2010 Redistributable, so we are not going to point you at one. Get it from the publisher directly. That matters more than usual here, because this is precisely the file the DLL download sites target.