Another question about DLLs

[winrawr]

So, supposing I do manage to compile a DLL with exports, how does the DLL work with my code? How would I check for the DLL on the system, and then, how would I link to it?
Also, Can a DLL written in C++ be used in a VB application?
I'm trying to write a script interpreter... sort of like python actually... Basically I want a DLL that a program can link to that will parse lines of code, or run through a script and parse each line, etc. and for each function that the script calls, there will be an equivalent function that the program calls to carry out that function. But I want the ability to add functions to the language from the application that will be using the DLL, would functions of different languages be compatible?
Like,

vb program                dll
----------------------------------------------------
send code to dll----->    parse code
                              |
                              v
                          code contains a function,
                          that isn't contained in the DLL
                              |
list of functions in   <------/
program
      |
      v
corresponding function,
user-defined in the
VB program--process the
passed argument here
      |
      \-------------->    return value sent back
                          to the parsing function

am I able to call functions between DLL and program, regardless of the language the program using the DLL is written in? Is there anything special about returning values back and forth between DLLs? can it be just like if the functions were all contained in the same code?
What can I not do if I expect the DLL to be portable between languages?
My main concern is like, if I have the parse function in the DLL, int parse(char* value); and then try and call it from visual basic, which doesn't (to the extent of my knowledge) have a char data type, what would happen? are the C++ string data type and the VB string data type interchangeable?

What if, in the DLL, I had a

class interpreter01{
...
} interpreter;

when I linked to the DLL, would "interpreter" of type "interpreter01" be available to the program already?
Right now my basic idea of a DLL is more or less equivalent to an #include statement.

[Stefano Mtangoo]

I'm not too far in C++ but most DLL stuffs, I read when I was learning Python's ctypes. Many of your questions seems to have Yes answer but again not solid in C++ and DLL. One question I can boldly answer

Can a DLL written in C++ be used in a VB application?
Answer is YES but I remember there is a little declaration stuffs.

[winrawr]

hmm that's good...how would I implement it though?

[winrawr]

anyone know just the basics of compiling a dll which exports a class and a function? Just like a short code? Also how to write the exports file

[Freaky_Chris]

One is even on C++ DLLs with VB!

Chris