/* BRAIN BOX MAIN.CPP */

#include "BrainBox.h"

....


/* Run the program Loop */
GUI_APP_MAIN
{	
	splashScreen().Run();
	Ctrl::ProcessEvent();

	// Open the mainWindow
    mainWindow().Run();
}

#ifndef _BrainBox_BrainBox_h_
#define _BrainBox_BrainBox_h_

#include <CtrlLib/CtrlLib.h>
#include <Core/Core.h>
#include <stdio.h>


using namespace Upp;


//Load Layouts
#define LAYOUTFILE <BrainBox/Layouts.lay>
#include <CtrlCore/lay.h>


// Load Images
#define IMAGECLASS Images
#define IMAGEFILE <BrainBox/images.iml>
#include <Draw/iml.h>




// Declarations
//Guessing some sort of declaration for the function needs to be made here?

#endif

/* Splash Screen File */
#include <CtrlLib/CtrlLib.h>

using namespace Upp;

struct splashScreen : TopWindow
{
	splashScreen()
	{
		Title("Splash Screen");
		SetRect(0, 0, 200, 300);
	}
};

C:\MyApps\BrainBox\main.cpp(119) : error C2228: left of '.PopUp' must have class/struct/union
        type is ''unknown-type''
C:\MyApps\BrainBox\main.cpp(119) : error C3861: 'splashScreen': identifier not found
main.cpp

class bar;   //a trick how to use class "bar" in other header without it's actual definition, see a bit down

class foo
{
protected:   //next definitions will be visible only inside the class and derived classes
  int x;     //variable definition
  bar *pointer_to_class_bar;   //you can use pointer even without actual definition of "bar" being known here

public:      //next definitions will be visible outside of the class
  foo() : pointer_to_class_bar(NULL)
  {
    //this is constructor - with (empty) code defined HERE */

    //pointer_to_class_bar->DoSomething();
    //^^ this would produce error, because compiler doesn't know here the bar has method "DoSomething"
  }

  int fwd_foo( int );  //this is forward definition of function, without actual code
};

#include "bar.h"   //in this file we will need to know bar class,
                   //so include it's full definition (similar file to foo.h)
#include "foo.h"   //include public definitions of foo class

//here comes the rest of foo implementation, like the missing body of int fwd_foo( int ) method

int foo::fwd_foo( int )  //notice how the name of method is preceded by class name
{
  if ( pointer_to_class_bar != NULL ) pointer_to_class_bar->SomeMethodOfBar();
  //^^ here it will work
  return 7;
}

#include "foo.h"   //we want to use foo class

...  inside some function like main for example ...
{
  foo Foo;   //create instance of class foo at function stack memory
  int y = Foo.fwd_foo( 0 );
  //^^ compiler knows how to call this method, because it was forward-defined in the "foo.h", and we did include that file
  //int my_x = Foo.x;
  //^^ error: while compiler knows the Foo has "x", you can't access it directly like this,
  //it's protected only for usage from withing Foo class family

  //bar Bar;  //this will create error, because compiler doesn't know full definition of class bar
  bar * another_bar_pointer;  //but this will work, because it was also forward-defined in foo.h,
  //but the usage is very limited, like only passing around the pointer value
  /* notice we don't need to include full bar.h to do that, 
     so we will save compile time and when you edit bar.h,
     this file does not need to recompile, only files which do include full bar.h,
     like foo.cpp
  */
}