more header files

I am learning C++ and I am trying to link files together. I know in general how files are linked (did it for a Unix class) but I've noticed that when data structures are introduced, it makes things a lot more difficult. For the life of me, I cannot figure out how to split the program (below) into three files: main.cpp, expand.cpp, and expand.h

The program below is the working program in one file. When I split it up into modules, I get all sorts of access violations and the blue screen of death. I have the two source files in /MyProjects, and the header in /Include (I've also tried keeping it in /MyProjects).

I use Dev C++ and Windows. Any guidance would be appreciated.



#include <iostream>
#include <list>
#include <cstdlib>

using namespace std;

class resources {
private:
float fertility;
public:
float GetFertility() { return fertility; }
void SetFertility( float f ) { fertility = f; }
};

class terrain {
private:
int terrain_type;
public:
int GetTerrain() { return terrain_type; }
void SetTerrain( int t ) { terrain_type = t; }
};

class world : public resources, terrain {
private:
int x, y;
public:
int Getx() { return x; }
int Gety() { return y; }
void Setxy( int a, int b ) { x = a; y = b; }
};

void ExpandMap( list<world> &ob )
{

list<world>::iterator p;

p = ob.begin();

p->Setxy(2,3);
cout << "X and Y: " << p->Getx() << ' ' << p->Gety() << endl;

}

int main()
{

list<world> map;
list<world>::iterator p;

map.push_back();

ExpandMap( map );

p = map.begin();
cout << "\n\nMAIN: X and Y: " << p->Getx() << ' ' << p->Gety() << endl;

system("PAUSE");
return 0;

}

I'll give it a shot

> expand.h
// Contains the three classes resources, terrain and world
// The function prototype
void ExpandMap( list<world> &ob );

> expand.cpp
#include <iostream>
#include <list>
#include <cstdlib>
#include "expand.h"
// And the function declaration
void ExpandMap( list<world> &ob ) {
// code
}

> main.cpp
#include <iostream>
#include <list>
#include <cstdlib>
#include "expand.h"
// And the function declaration
int main ( ) {
// code
return 0;
}

Thank you Salem!

Just one more question for right now. I noticed that you put the #include <list> in expand.cpp but not expand.h. That confused me because I assumed expand.h would have to 'see' the <list> because of this prototype in the header file:

void ExpandMap( list<world> & );

With a little playing around I've discovered that the code compiles and runs whether <list> is in expand.cpp, expand.h, or both.
Can you provide any information on how header files are 'seen' by the various parts of the code?

Thanks again.