cant get dialog to return a value

i cant get my dialog to close and return a value. What method do i use to force the dialog to close? here is the code in my parent class. if i close the dialog using OnOK() no message box is displayed in the code below.

             mainDlg dlg;
            m_pMainWnd = &dlg;
            INT_PTR nResponse = dlg.DoModal();
            if (nResponse == IDOK)
            {
                  // TODO: Place code here to handle when the dialog is
                  //  dismissed with OK
                  AfxMessageBox("ok");
            }
            else if (nResponse == IDCANCEL)
            {
                  // TODO: Place code here to handle when the dialog is
                  //  dismissed with Cancel
                  AfxMessageBox("cancel");
            }
            else AfxMessageBox("crap");