You mean their MSVC from 2012. They only just added support for C99 with the lat...

pjmlp · on Feb 9, 2015

Because C is legacy on Windows. No need for C when there is C++, which also allows for safer systems programming.

The C99 subset that was added was what is required by C++11/C++14 standards and some key customers.

There are no plans for full ANSI C compliance, as discussed here

mmozeiko · on Feb 9, 2015

They added some support for C99. It is still missing bunch of stuff. Like "static" in array parameter index.

cowsandmilk · on Feb 9, 2015

and even then, I think their implementation of complex.h is screwball.