Thanks Neurosys very valuable post.
There is one case still unclear.
However i try to pass to my digits a value from a variable (type var).
But whatever i put, my panel display a 0.00000 value.

Here is a code snippet.
Can someone please explain me where it's wrong.

Code:
#include "stdafx.h"
#include "GreySandBox.h"
#define WIN32_LEAN_AND_MEAN 
#include <windows.h>
#include <stdlib.h>
#include <stdio.h>
#include <malloc.h>
#include <memory.h>
#include <tchar.h>
#include <string.h>

// Include the engine data types, variables, and functions
#include "adll.h"




PANEL* pPanel;
var a = 4;
var b = 5;



int APIENTRY _tWinMain(HINSTANCE hInstance,
HINSTANCE hPrevInstance,
LPTSTR lpCmdLine,
int nCmdShow)
{ 


	//Open the GameStudio Engine
	ENGINE_VARS *ev = engine_open(NULL);

	//Initialize The Graphics Environment
	video_set(_VAR(1280),_VAR(1024),_VAR(32),_VAR(0));
	
	

	//Create panel and digits
	pPanel = pan_create("digits(0,10,\"A = %f\",*,1,a;\
digits(0,20,\"B = %f\",*,1,b);",_VAR(1));
	pPanel->flags |= VISIBLE;
	pPanel->pos_x = _VAR(0);
	pPanel->pos_y = _VAR(0);


	//Main Loop
	while (engine_frame()) {

		if (v(key_esc)) { sys_exit(""); }
	}
	
	engine_close();
	//Exit the application with code 0
	return 0;
}