[WinApi] Problem z rejestrowanie klasy

#include <windows.h>

int WINAPI WinMain( HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow )
{
    LPSTR nzwkla = "Okn";
    WNDCLASSEX wc;
    wc.cbSize = sizeof( WNDCLASSEX );
    wc.style = 0;
    wc.lpfnWndProc = WNDPROC;
    wc.cbClsExtra = 0;
    wc.cbWndExtra = 0;
    wc.hInstance = hInstance;
    wc.hIcon = LoadIcon( NULL, IDI_APPLICATION );
    wc.hCursor = LoadCursor( NULL, IDC_ARROW );
    wc.hbrBackground =( HBRUSH )( COLOR_WINDOW + 2 );
    wc.lpszMenuName = NULL;
    wc.lpszClassName = nzwkla;
    wc.hIconSm = LoadIcon( NULL, IDI_APPLICATION );
    if( !RegisterClassEx( & wc ) )
    {
        MessageBox( NULL, "Wysoka Komisja odmawia rejestracji tego okna!", "Niestety...",
        MB_ICONEXCLAMATION | MB_OK );
        return 1;
    }
    HWND hwnd;
    hwnd = CreateWindowEx( WS_EX_WINDOWEDGE, nzwkla, "Okno", WS_CAPTION, CW_USEDEFAULT, CW_USEDEFAULT, 800, 600, NULL, NULL, hInstance, NULL );
   
    ShowWindow( hwnd, nCmdShow );
    UpdateWindow( hwnd );
    if( hwnd == NULL )
    {
        MessageBox( NULL, "Nie utworzono!a", "Nie utworzono!b", MB_ICONEXCLAMATION | MB_OK );
    }
    return 0;
}