Вопросы API-программирования

#include <windows.h>

LRESULT CALLBACK WndProc(HWND hwnd,UINT mes,WPARAM wp,LPARAM lp) {
switch(mes) {
case WM_QUIT: return(0);
case WM_CLOSE:
   MessageBox(NULL,"Пришло WM_CLOSE, закрываемся.","Перехват",MB_OK|MB_SETFOREGROUND|MB_ICONASTERISK);
   PostQuitMessage(0);
   break;
case WM_NCDESTROY:
case WM_DESTROY:
   MessageBox(NULL,"Вот он где, ваш WM_DESTROY!","Перехват",MB_OK|MB_SETFOREGROUND|MB_ICONEXCLAMATION);
   SetActiveWindow(hwnd);
   return(1);
case WM_COMMAND: switch(LOWORD(wp)) {
   case 101:
      PostMessage(hwnd,WM_DESTROY,0,0);
      break;
   case 102:
      PostMessage(hwnd,WM_CLOSE,0,0);
   }
} 
return(DefWindowProc(hwnd,mes,wp,lp));
}//============================================================================

int WINAPI WinMain(HINSTANCE hi,HINSTANCE hpi,LPSTR cmd,int ncmd) {
int res=1;
MSG msg;
WNDCLASSEX w;
LOGBRUSH brush;
HWND mainwin;
int i;
LPSTR CLASS_NAME="TMP_CLASS";
LPSTR BUTTONCLASS="BUTTON";

brush.lbStyle=BS_SOLID;
brush.lbColor=RGB(0xC0,0xC0,0xC0);
memset(&w,0,sizeof(WNDCLASSEX));
w.cbSize=sizeof(WNDCLASSEX);
w.style=CS_HREDRAW|CS_VREDRAW;
w.lpfnWndProc=WndProc;
w.hInstance=hi;
w.cbWndExtra=36;
w.hbrBackground=CreateBrushIndirect(&brush);
w.lpszClassName=CLASS_NAME;
RegisterClassEx(&w);

mainwin=CreateWindowEx(WS_EX_LEFT,CLASS_NAME,"Перехватываем WM_DESTROY",
WS_CAPTION|WS_POPUP,30,10,320,200,NULL,NULL,hi,NULL);

CreateWindow(BUTTONCLASS,"WM_DESTROY",
WS_CHILD|BS_CENTER|WS_TABSTOP|BS_PUSHBUTTON|WS_VISIBLE,
24,138,130,28,mainwin,(HMENU)101,hi,NULL);

CreateWindow(BUTTONCLASS,"WM_CLOSE",
WS_CHILD|BS_CENTER|WS_TABSTOP|BS_PUSHBUTTON|WS_VISIBLE,
164,138,130,28,mainwin,(HMENU)102,hi,NULL);

ShowWindow(mainwin,SW_SHOW);
while(res) {
   res=GetMessage(&msg,NULL,0,0);
   TranslateMessage(&msg);
   DispatchMessage(&msg);
}
return(0);
}