Modules and Member Functions

I have 3 files: stack.h, calc,c and stack.c

Code:

void make_empty(void);
int is_empty(void);
int pop(void);

Code:

#include "stack.h"
main() {
     make_empty();
     ...
}

Code:

#include "stack.h"
int contents[100];
int top = 0;
//function definitions

I get that stack.h is the interface, calc.c is the client and that stack.c is the implementation of the module. My question is: What exactly is the module? The definition is "a collection of services", so I thought that would be stack.c, but it isn't?

Also if you can access data members of a structure using the . and -> operator, why can't you use it with objects and member functions?

Code:

struct blah{
    int a;
    int b;
};

blah *abc;
abc->a = 0;

Since -> means (*abc).a, why can't you use it when calling member functions outside the class?

Code:

class Fraction {
   int denom;
   int num;

public:
   void reduce();
};

Fraction *f1, *f2;
f1->reduce();

why can't you use it when calling member functions outside the class?

you can

hehe, oops... must have zoned out when the prof was explaining it.
Thanks for clearing that up!