trying to compile a dll

I am trying to compile my first dll file. at home I tried with Borland Free Compiler, but do not know the options to specify and can't find, if someone could tell me this also please let me know.

Now at uni, i try to compile with visual C and am getting an error:

:\temp\myproj\testdll.h(15) : error C2059: syntax error : 'string'

this is the offending code

#define MYLIBAPI extern "C" __declspec(dllexport)

MYLIBAPI DWORD g_nResult;

this is the method according to 'programming apps for windows' by Richter, p 689

any help appreciated