Hi all. What would be a way to program a code that created txt files in any dir after %systemroot% ?

For example. If you were to type cd %systemroot% in an XP command line, then you would get sent to C:\WINDOWS - Im trying to find out a way to create files in that directory, no matter the drive. Ive tried the following code:

#include <fstream>
using namespace std;

void main(){
ofstream file;
file.open("%systemroot%\\test.txt");
file << "This is only a test." << endl;
file.close();
}

And nothing happens. So i switched %systemroot% to %windir% from another persons example, and it didnt work either. So i was hoping maybe im using a wrong character. (ie: %) Maybe if im using another character then i'll succeed. Any suggestions will be greatly appreciated. Thanx in advance!