HWND ButtonHandle;
if( (wnd = FindWindow(0, "Do you want to save?")) )
{
   ButtonHandle = FindWindowEx(wnd, 0, "SaveButton", "&Save");
   SendMessage(wnd, WM_COMMAND, MAKEWORD(GetDlgCtrlID(ButtonHandle), BN_CLICKED ), (LPARAM)ButtonHandle);

}

SendMessage(ButtonHandle, BM_CLICK, 0, 0);

SendMessage(ButtonHandle, WM_LBUTTONDOWN, 0, 0);
SendMessage(ButtonHandle, WM_LBUTTONUP, 0, 0);

SendMessage(ButtonHandle, BM_CLICK, 0, 0);

HWND buttonHandle = 0;

BOOL CALLBACK GetButtonHandle(HWND handle, LPARAM)
{
 char label[100];
 int size = GetWindowTextA(handle,label,sizeof(label));
 if(strcmp(label,"&Save") == 0)
 {
  buttonHandle = handle;
  return false;
 }
 return true;
}
void main()
{
 HWND windowHandle = FindWindowA(NULL,"Do you want to Save?");
 if(windowHandle != 0)
 {
  BOOL ret = EnumChildWindows(windowHandle,GetButtonHandle,0);

  if(buttonHandle != 0)
  {
   LRESULT res = SendMessage(buttonHandle,BM_CLICK,0,0);
   //SendMessage(buttonHandle,WM_LBUTTONDOWN,0,0);
   //SendMessage(buttonHandle,WM_LBUTTONUP,0,0);
  }

 }



}

SendMessage(btnHandle, WM_LBUTTONDOWN, 0, 0);
SendMessage(btnHandle, WM_LBUTTONUP, 0, 0);
SendMessage(btnHandle, WM_LBUTTONDOWN, 0, 0);
SendMessage(btnHandle, WM_LBUTTONUP, 0, 0);

void CMyClass::OnMessageY(CWnd *cwnd)
{
    CBaseClass::OnMessageY(cwnd);
    //... my code
}

HWND ButtonHandle;
if( (wnd = FindWindow(0, "Do you want to save?")) )
{
    SendMessage(ButtonHandle, WM_LBUTTONDOWN, MK_LBUTTON, 0);
    SendMessage(ButtonHandle, WM_LBUTTONUP, MK_LBUTTON, 0);
}