I dont know how to do it in C++ but to open a new command prompt window that is also minimized (or “hidden”) using a batch file i would use:
start /min cmd
Or if you start the command prompt you can type:
@echo off
cls && start /b cmd
This restarts the current command prompt window with out closing it, however all previously set environment variables are reset. Hope this helps!
(PS. This was tested and was successful on Windows 7 Ultimate OS)