SSRS Multi select parameter

Can anyone explain how you declare a parameter in a class as an array of values to be selected from in a where clause.

My class query wants to select where AccountNum in (‘C0001’,‘C0005’,‘C0012’). These are the account numbers selected from the drop down multi select on the SSRS report.

So I would expect the code in my class to be as follows:-

select * from custTransTotalSales

where custTransTotalSales.AccountNum in contract.parmAccountNum()

So I need the correct syntax for the above statement and the declaration for contract.parmAccountNum()

Once I used thistutorial : http://arshkal.wordpress.com/2012/04/27/creating-multi-select-lookup-dialog-for-ssrs-report-parameter-in-ms-dynamics-ax-2012/

But I think it is easier if you build an AOT Query and use the query as parameter, They will be able to select multiple values and also they could add ranges to other fields if needed.