🚀 go-pugleaf

I am having a terrible time getting the IDE to accept a Filter String
comparing a TDate field from IDE (dBase).  I'm using CBuilder3.0 Pro.
Here is basically what I want to compare:

FilterString = "(EFFDATE >= " + mbdate + ")  AND (EFFBDATE <= " + medate +
")";

I have tried &mbdate and also tried (double) mbdate and (int) mbdate, etc.
In these cases produced "improper pointer addition" among other errors.

Explanations:
FilterString is a ANSI String variable.
mbdate is a TDate memory variable. (means beginning date of a certain
period).
medate is a TDate memory variable  (means ending date of a period)
EFFDATE is a dBase date field (means effective date)

This string (and many, many others that are similar) will compile, but cause
the program to encounter a runtime error, something to the effect:
illegal filter string
illegal character '/', etc.

I have looked everywhere in the help system on this, but have found nothing
to tell me how to refer to and compare TDate fields in a filter string.
I appreciate any help you might be able to provide regarding this problem.

Cary