[WinAPI] Wiele okienek

#include <windows.h>
#include <commctrl.h>

HWND hButton, hWnd, hWndChild;

LRESULT CALLBACK WndProc( HWND, UINT, WPARAM, LPARAM );
LRESULT CALLBACK WNDchild( HWND, UINT, WPARAM, LPARAM );

INT WINAPI WinMain( HINSTANCE hInstance, HINSTANCE, LPSTR lStart, INT nShow )
{
    WNDCLASSEX wc;
    wc.hInstance = hInstance;
    wc.lpszClassName = "Parent";
    wc.lpfnWndProc = WndProc;
    wc.style = 0;
    wc.cbSize = sizeof( WNDCLASSEX );
    wc.hIcon = LoadIcon( 0, IDI_APPLICATION );
    wc.hIconSm = LoadIcon( 0, IDI_APPLICATION );
    wc.hCursor = LoadCursor( 0, IDC_ARROW );
    wc.lpszMenuName = 0;
    wc.cbClsExtra = 0;
    wc.cbWndExtra = 0;
    wc.hbrBackground =( HBRUSH ) GetStockObject( WHITE_BRUSH );
    if( !RegisterClassEx( & wc ) ) return 0;
   
    WNDCLASSEX wcp;
    wcp.hInstance = hInstance;
    wcp.lpszClassName = "Child";
    wcp.lpfnWndProc = WNDchild;
    wcp.style = 0;
    wcp.cbSize = sizeof( WNDCLASSEX );
    wcp.hIcon = LoadIcon( 0, IDI_APPLICATION );
    wcp.hIconSm = LoadIcon( 0, IDI_APPLICATION );
    wcp.hCursor = LoadCursor( 0, IDC_ARROW );
    wcp.lpszMenuName = 0;
    wcp.cbClsExtra = 0;
    wcp.cbWndExtra = 0;
    wcp.hbrBackground =( HBRUSH ) GetStockObject( WHITE_BRUSH );
    if( !RegisterClassEx( & wcp ) ) return 0;
   
    hWnd = CreateWindowEx( 0, "Parent", "rodzic", WS_SYSMENU, 20, 20, 600, 300, 0, 0, hInstance, 0 );
    hButton = CreateWindowEx( 0, WC_BUTTON, "Przycisk1", WS_CHILD | WS_VISIBLE, 480, 90, 100, 30, hWnd,( HMENU ) 1, hInstance, 0 );
    hWndChild = CreateWindowEx( 0, "Child", "Okno potomne", WS_SYSMENU, 20, 20, 600, 300, hWnd, 0, hInstance, 0 );
   
    UpdateWindow( hWnd );
    UpdateWindow( hWndChild );
    UpdateWindow( hButton );
    ShowWindow( hWnd, nShow );
    ShowWindow( hButton, SW_SHOW );
   
    MSG msgs;
    while( GetMessage( & msgs, 0, 0, 0 ) )
    {
        TranslateMessage( & msgs );
        DispatchMessage( & msgs );
    }
    return msgs.wParam;
}

LRESULT CALLBACK WndProc( HWND hwnd, UINT msg, WPARAM wPar, LPARAM lPar )
{
    if( msg == WM_COMMAND )
    {
        if( wPar == 1 )
        {
            ShowWindow( hWndChild, SW_SHOW );
        }
    }
    if( msg == WM_CLOSE )
    {
        if( hwnd == hWndChild )
        {
            ShowWindow( hWndChild, SW_HIDE );
        }
        if( hwnd == hWnd )
        {
            DestroyWindow( hButton );
            PostQuitMessage( 0 );
        }
    }
    else
    {
        return DefWindowProc( hwnd, msg, wPar, lPar );
    }
    return 0;
}

LRESULT CALLBACK WNDchild( HWND hwnd, UINT msg, WPARAM wPar, LPARAM lPar )
{
    switch( msg )
    {
    case WM_PAINT:
        break;
    case WM_CLOSE:
        ShowWindow( hwnd, SW_HIDE );
        break;
        default:
        return DefWindowProc( hwnd, msg, wPar, lPar );
    }
    return 0;
}