I am not very well-versed with .NET but i know Crystal.
How you pass a variable to crystal depends on how you need to use the variable. Is it a parameter to its data source? Or is it a value that you want to use in the report?
If the former, there is a data source parameter collection in the crystal report object and you just need to pass the value into each parameter property.
If the latter, what i would do is create a formula in the crystal report and in the code I would populate this formula, which is exposed through a collection, with the value you want to pass.
Hope this helps.
Bernard L. Omiple
VFP, SQL Server, Crystal Reports