Windows: Vensim ships with a default mdl.bat file that should work with most versions of Microsoft Visual Studio C/C++. There are many versions, so there are commented lines in mdl.bat that should work with most alternatives. If you need something different simply add and remove comment markers (REM statements).
Macintosh: Vensim ships with the script file mdl.macx. This should work as is so long as you have gcc installed. gcc is an optional component on the Mac so you may need to install it.
