How to pass parameter values to a select case?

Hi to all,

1- I’m not sure if this is possible and how do we perform this if so

2- We have this Select Case in a Data Item which contains the 12 month of the year as each case statement

3- Every month we have to open the Cognos Report Studio report (version 10.1.1) in design mode and manually indicate a sales amount next to the correct concerned month

4- Here is how the Select Case is set:
CASE [num_mth]
WHEN 1 THEN 10
[size=10pt]WHEN 2 THEN 11[/size]
WHEN 3 THEN 0
WHEN 4 THEN 0
WHEN 5 THEN 0
WHEN 6 THEN 0
WHEN 7 THEN 0
WHEN 8 THEN 0
WHEN 9 THEN 0
WHEN 10 THEN 0
WHEN 11 THEN 0
WHEN 12 THEN 0
END

5- Which if we are in March, we have to enter a sales number (coming from a confidential paper copy) next to the last completed month (2: February). In our case the amount of 11$

QUESTION:
I know how to use prompts in order to pass the value entered by the user to a specific filter of the query.
But, is it possible to use that same logic to pass the value entered by the user directly in the correct select satement,for example mnext to ‘WHEN 3’ by using some kind of Report variable or so ??