Update date records with dateAdd()

I know I cannont do this with Coldfusion without multiple steps, but I think I should be able to accomplish it with a stored procedure. My question is how?

I have a couple of variables:

@groupID int, // the group identifier
@newdatediff int // the number of days to add

I want to update the different iDate dates using dateAdd() and the newdatediff number. I'm guessing here:

SET iDate = dateAdd([day], @newdatediff, iDate)

I have limited knowledge of how to set it up as you can tell. Any help would be greatly appreciated.

Thanks,
Doug