Crystal Reports Dateadd function

Message

     Hello,
I have a field that is varchar2 in the backend, the data is entered in dd/mm/yyyy format (this is a user defined field that the user used to store data). I need to add 90 days to dd portion of the data.
When I use Dateadd('d', 90,cdate({TABLE.DESC2}), I get into issues when I write formulas else where. I thought may be I should use variables to first convert to date and then do the add, below is what I put together: 
datevar XDATE:= cdate({TABLE.DESC2});
datevar CONVDATE:=dateadd('d', 90, XDATE)

In my second line I get an error, it says date is rewuired here.

Can someone please suggest me a better way to deal with this issue?

Thanks.