To call fortran library from LabWindows and C\C++ you should know the functions prototypes
the simplest way - get function decription from its fortran code and create C header file. If you do it, you should have a lib file, wich contains definition of fortran function. It creates togeter with dll file during compilation.
If you have no lib file, you may use LoadLibrary function to load dll file into computers memory.
Then you call GetProcAddress to get addres of function you want to use
call it.
For this method you should define type of pointer to function
int (*pt2Func)(float, char, char)