Lazy evaluation in SSRS - vba

Question

I'm using SSRS 2005 to produce a report, and one of the columns in my report is a simple mean calculation. I don't want to divide by zero, so for the textbox value I have put:
=Switch(Fields!Count.Value=0,0,Fields!Count.Value>0,Fields!Sum.Value/Fields!Count.Value)
This still evaluates the second expression.
And so does:
=IIF(Fields!Count.Value=0,0,Fields!Sum.Value/Fields!Count.Value)
I don't want my report to display errors. How can I overcome this issue?

Answer 1

Unfortunately because IIF is actually just a function, all arguments get evaluated before the function gets called (resulting in your divide by zero).
One way of embedding complex logic in an expression is to embed a function in the report. You can write a VB function to return whatever you like in the Code Tab of the Report Properties.
Public Function GetMeanValue(ByVal Sum as Decimal, ByVal Count As Int) As Decimal
'your logic in plain old vb syntax here
End Function
In the Textbox Text expression property:
=Code.GetMeanValue(Fields!Sum.Value, Fields!Count.Value)

Answer 2

When checking for zeros, I always negate the expression like this:
=IIF(Fields!Count.Value<>0,Fields!Sum.Value/Fields!Count.Value,0)
This has the added benefit of avoiding the division in case the Count field is empty/null.

Answer 3

Try this:
=IIf(Fields!Count.Value = 0, 0, Fields!Sum.Value / IIf(Fields!Count.Value = 0, 1, Fields!Count.Value))

Answer 4

Here is solution that has always worked for me:
Avoiding Divide By Zero Errors .
It gets tedious if the report has too many divisions. I prefer some vb code to do the division and handle division by zero. Not sure if too much of vb code would bring down the performance of the report.
Here is how to do it with vb
Replaced he link with archive.org link. Here is the relevant content from that link:
Instead of dropping that calculation into all the textboxes that are
doing division I go under Report >> Report Properties >> Code and
drop in the following code:
Public Shared Function Divide(Num1 as double, Num2 as double) AS
object
IF ISNOTHING(Num2) Or Num2 = 0 Then
Divide = "n/a"
ELSEIF Num1 = 0 THEN
Divide = 0
ELSE
Divide = Num1 / Num2
END IF
End Function
And then in each of the textboxes on the report where I need to do
division, I call the function like this:
=Code.Divide(1, 0)