#Error using IIF and divide by zero

Question

I am getting an error in a calculated field that could potentially divide by zero, even though I'm using an IIF.  The column displays in the report as "#Error".  My expression looks like this:
= IIF(Fields!Qty.Value = 0,
"None", Fields!Hours.Value / Fields!Qty.Value)
I have successfully used this approach with INT fields, but this time the Hours field is a NUMERIC(9,2).  My workaround is to do this:
 IIF(Fields!Qty.Value = 0, "None", IIF(Fields!Qty.Value = 0, 42, Fields!Hours.Value) / Fields!Qty.Value)
I guess the 42 is cast to an INT inside the second IIF and the calculation works.
What's strange is that the division would even be carried out in the event of Qty = 0 from the first IIF, because the expression should just evaluate to "None" and that would be that.
Has anybody run into this problem?  Is my workaround the recommended approach?
-Larry

Answer 1

First a diatribe: This is just one of the many annoying "features" of SSRS that needs to be fixed. It should just flat out work. Period.
Now the fix.
The following formula to calculate Discount% gives the #Error result if List = 0
=iif(Fields!List.Value=0,0, (Fields!List.Value-Fields!Net.Value)/Fields!List.Value)
However, if you add a very small number to the divisor it will work.
=iif(Fields!List.Value=0,0, (Fields!List.Value-Fields!Net.Value)/(Fields!List.Value+.000001))
Apparently SSRS evaluates the false part of the expression before it tests. Try this in most any other language and you will not have this problem.
You just need to add a small enough number to your formula to not impact your results when the divisor is not zero.
You can actually leave out the IIF entirely if you do this:                             
Fields!List.Value-Fields!Net.Value)/(Fields!List.Value+.000001)
I usually leave the syntax in there just so I know what the intention was.