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.