关于编译的小问题！

Question

我做了个日历程序，用了ActiveX的Calendar Control 8.0想让鼠标双击日历后出现选择的日期提示，可是最后编译不过去，给出双击的代码望高手指点！
void CVcDlg::OnDblClickCalendar1() 
{
// TODO: Add your control notification handler code here
CString cSelectedDate;
char * cDay = " "; 
char * cYear = " ";itoa(m_Calendar1.GetDay(),cDay,10);
cSelectedDate=cDay;switch(m_Calendar1.GetMonth())
{
case 1:
cSelectedDate=cSelectedDate+"January";
break;
case 2:
cSelectedDate=cSelectedDate+"February";
break;
case 3:
cSelectedDate=cSelectedDate+"March";
break;
case 4:
cSelectedDate=cSelectedDate+"April";
break;
case 5:
cSelectedDate=cSelectedDate+"May";
break;
case 6:
cSelectedDate=cSelectedDate+"June";
break;
case 7:
cSelectedDate=cSelectedDate+"July";
break;
case 8:
cSelectedDate=cSelectedDate+"August";
break;
case 9:
cSelectedDate=cSelectedDate+"Septermber";
break;
case 10:
cSelectedDate=cSelectedDate+"October";
break;
case 11:
cSelectedDate=cSelectedDate+"November";
break;
case 12:
cSelectedDate=cSelectedDate+"December";
break;
}
itoa(m_Calendar1.GetYear(),cYear,10);
cSelectedDate=cSelectedDate+cYear;AfxMessageBox("You double-clicked on:" + cSelectedDate , MB_OK | MB_INFORMATION, 0);
}问题出在最后的MB_INFORMATION上，提示：error C2065: 'MB_INFORMATION' : undeclared identifier
可是教材上就是这么写的！求教！