Where are the operating system environment variables stored? How can I get it through a program?

Getenvironmentvariable
Expandenvironmentstrings support hull
Setenvironmentvariable

HKEY_LOCAL_MACHINE // system /// CurrentControlSet /// control /// settion manager /// Environment
HKEY_CURRENT_USER of the current user // Environment

I have pasted the complete program. If you have time, run it in turboc2.
# Include // "stdio. h
# Include // "Io. h //"
# Include // "stdlib. h //"
Main ()
{
/* Define variables */
Int accmode;
Const char * envname = // "WINDIR //";
Char * envvalue;
/* Assign default value */
Accmode =-1;
Envvalue = getenv (envname );
/* Print setup title */
Printf (// "will setup. NET Framework... // N //");
/* Detect if there is. NET Framework v1.41 installed */
Access (envvalue, accmode );
Printf (// "accmode is % d // N //", accmode );
Printf (// "WINDIR is % S //", envvalue );
If (accmode = 0)
Printf (// "there is C: // windows //");
}