This worked for me:

1. put this in the header of your DLL

#ifdef MYDLL_EXPORTS
#define MYDLL_API __declspec(dllexport)
#else
#define MYDLL_API __declspec(dllimport)
#endif

#ifdef __cplusplus
extern "C" {
#endif
MYDLL_API int fnMyDll(int num);
#ifdef __cplusplus
}
#endif

2. put this in the header of your calling program

#ifdef MYDLL_EXPORTS
#define MYDLL_API __declspec(dllexport)
#else
#define MYDLL_API __declspec(dllimport)
#endif

MYDLL_API int fnMyDll(int num);

MYDLL_EXPORTS is a compiler flag that gets set when you compile as a DLL.
Your function gets defined as an export within the DLL, but as an import within the calling program.

3. Then call the function normally.

int liRslt = fnMyDll(0);

Hope this helps,
Ken