VC调用Excel的退出问题？

以下是本人在编译环境为VS2010，Excel为2010环境下编写的一段代码，执行后，
Excel进程无法关闭，参考了网上的许多措施，也无法关闭Excel进程，望高手指点！
谢谢！！！
CString FilePathName;
CFileDialog dlg(true,NULL,NULL,OFN_HIDEREADONLY|OFN_OVERWRITEPROMPT,
_T("EXCEL文件(*.xls；*.xlsx)|*.xls;*.xlsx||"),AfxGetMainWnd());

if(dlg.DoModal()==IDOK)
{

FilePathName=dlg.GetPathName();
CApplication app;
CWorkbook book;
CWorkbooks books;
CRange range;
CWorksheets sheets;
CWorksheet sheet;
COleException* pe = new COleException;
if (!app.CreateDispatch(_T("Excel.Application"),pe))
{
MessageBox(_T("Error!Creat Excel Application Server Faile!"));
exit(1);
}
app.put_Visible(true);

books = app.get_Workbooks();
book = books.Add(_variant_t(FilePathName));

int num_Sheel;

sheets.AttachDispatch(book.get_Worksheets());
num_Sheel=sheets.get_Count();
sheet.AttachDispatch(sheets.get_Item(COleVariant((short)1)));
range = sheet.get_Range(COleVariant(_T("A1")),COleVariant(_T("A1")));
_variant_t var;
CString strResult;
int i,j;
i=1;
j=1;

var=range.get_Item(_variant_t(i),_variant_t(j));

range.ReleaseDispatch();
sheet.ReleaseDispatch();
sheets.ReleaseDispatch();

//结尾，释放
COleVariant covTrue((short)TRUE),covFalse((short)FALSE),covOptional((long)DISP_E_PARAMNOTFOUND, VT_ERROR);  
book.Close(covFalse,covOptional,covOptional);
books.Close();
pe->Delete();

book.ReleaseDispatch();
books.ReleaseDispatch();
app.Quit();
app.ReleaseDispatch();

MessageBox(_T("完成"),_T("提示"),MB_OK);
}