Dear .NET Developers

I need to provide an environment that users can build a formula usuin field names of a database
table and some string functions like "substr","left", and "right".The environment saves formula
in a string variable,and when user clicks a button,my code must run that formula over values of
those fields for selected record of that table.
Now,I have that environment and it returns formula as a sring to me,but I don't still have any
idea how to run this string.Do I have to write some code to compile it?I found that .Net has
some namespaces for building dynamic methods,I mean Document object model,but if I want to use
classes of this namesapce I have to convert that formula to IL,which is more difficult for me.
Is there any other idea how I can run a user defined expression inside my code and show up its
result to user?That expression can be like this,if we suppose all table field names start with
"fld":

"fldDKCode+fldDKSerial+Substr(fldDKDate,3,2)+fldDKId+Left(fldDKUserName,4)"

And I have a database table named TBDKUsers,includes all fields mentioned above.When user clicks
on Run button,my program must show the result of this expression for selected record of TBDKUsers.

Thanks you very much