You can either use _putenv()
which takes a string parameter as the string classSize=7
;
ostringstream classSize;
classSize << "classSize=" << howManyInClass;
_putenv(classSize.str().c_str());
...or (preferably) the security enhanced _putenv_s()
that takes the key and the value as separate (const char*) parameters;
ostringstream classSize;
classSize << howManyInClass;
_putenv_s("classSize", classSize.str().c_str());