//---------------------------------------------------------------------------
#include <Windows.h>
#include <Messages.hpp>
#pragma hdrstop
//---------------------------------------------------------------------------
#pragma argsused

  int iLeft = 100;
  int iTop = 100;
  int iWidth = 300;
  int iHeight = 200;
  char cClassName[] = "TCm_miso1";
  HINSTANCE hInstance=0;

LRESULT __stdcall WndProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam){
  LRESULT  Result = 0;
  HWND ID_OK;

  switch(uMsg){
    case(WM_CREATE):{
        ID_OK = CreateWindow("BUTTON", "OK-Button", WS_VISIBLE | WS_CHILD,
                    100, 100, 100, 30, hWnd, 0, hInstance, NULL);
        if(ID_OK == INVALID_HANDLE_VALUE)
          MessageBox(hWnd, "Button nicht erzeugt", "Meldung", 0);
    }
    case(WM_DESTROY): PostQuitMessage(0);
    case(WM_COMMAND):{
      if(HIWORD(wParam) == BN_CLICKED)
        if(LOWORD(wParam) == (WPARAM)ID_OK)
          MessageBox(hWnd, "OK Button gedrückt", "Meldung", 0);
    }
    default: Result = DefWindowProc(hWnd, uMsg, wParam, lParam);
  }
  return(Result);
}

int main(int argc, char* argv[])
{
  MSG msg;
  TRect rect;
  int deskh, deskw;
  NONCLIENTMETRICS ncm;
  HANDLE hWnd;
  WNDCLASSEX wc;

  hInstance=GetModuleHandle(NULL);  //NACHTRÄGLICH EDITIERT

  SetLastError(0);
  wc.cbSize = sizeof(wc);          // size of structure
  wc.style = CS_HREDRAW |CS_VREDRAW;// redraw if size changes
  wc.lpfnWndProc = &WndProc;     // points to window procedure
  wc.cbClsExtra = 0;                // no extra class memory
  wc.cbWndExtra = 0;                // no extra window memory
  wc.hInstance = hInstance;         // handle to instance
  wc.hIcon = LoadIcon(NULL,IDI_APPLICATION);// predefined app. icon
  wc.hCursor = LoadCursor(NULL,IDC_ARROW);// predefined arrow
  wc.hbrBackground = GetStockObject(WHITE_BRUSH);// white background brush
  wc.lpszMenuName =  "MainMenu";    // name of menu resource
  wc.lpszClassName = "MainWClass";  // name of window class
  SystemParametersInfo(SPI_GETWORKAREA, 0, &rect, 0);
  deskw = rect.Right - rect.Left;
  deskh = rect.Bottom - rect.Top;
  ncm.cbSize = sizeof(ncm);
  SystemParametersInfo(SPI_GETNONCLIENTMETRICS, sizeof(ncm), &ncm, 0);
  iWidth = iLeft + iWidth;
  iHeight = iTop + iHeight + ncm.iMenuHeight + ncm.iCaptionHeight;
  iLeft = (deskw / 2) - (iHeight / 2);
  iTop = (deskh / 2) - (iHeight / 2);

  if(!RegisterClassEx(&wc))
    return(GetLastError());

  hWnd = CreateWindow(
        "MainWClass",        // name of window class
        "Sample",            // title-bar string
        WS_OVERLAPPEDWINDOW, // top-level window 
        CW_USEDEFAULT,       // default horizontal position 
        CW_USEDEFAULT,       // default vertical position 
        CW_USEDEFAULT,       // default width 
        CW_USEDEFAULT,       // default height 
        (HWND) NULL,         // no owner window 
        (HMENU) NULL,        // use class menu 
        hInstance,           // handle to application instance 
        (LPVOID) NULL);      // no window-creation data

  if(!hWnd)return(GetLastError());

  while(1){
    if(!GetMessage(&msg, 0, 0, 0)) break; //oops :o)
    TranslateMessage(&msg);
    DispatchMessage(&msg);
  }

  return(GetLastError());
}
//---------------------------------------------------------------------------

Freundlichen Gruss
Michael

RegisterClassEx(&wc);
  HRESULT res=GetLastError();

Gruss
Michael

Grüsse Michael