Attach is a VS 2010 sample solution. It demonstrates how integers, reals, and character strings may be passed between Visual Basic to/from Fortran and C dll's, and to/from Fortran and C dll's as individual values and as arrays.
The program accepts 2 integers, 2 reals and 2 strings (10 characters max) as input. It returns integer 2 output as the product integer1 and integer 2, real 2 output as the product of real 1 and real 2, and concantenates the character strings with themselves with an underscore in between.
The Fortran code probably does not use the most up-to-date methods. Please feel free to submit new code which meets the latest standard.
The C code does not use the the latest safe functions like strcpy_s and sprintf_s. I'm just a novice C programmer. Again, feel free to update these C routines to the latest standard.