I dont have the code in front of me but there are a couple of ways to approach what you want.
The first is parameters are a collection in CR so you can refer to the parameters by their name or index and assign the value of the VS control to parameter. You do need to take care with the data types so as to avoid the mismatch error.
The second way would be to create your report and populate it with report items such as textboxes. You can give these items names perhaps to match your VS naming conventions. The text controls can be referenced, I believe within the report defintions class, then pass the value into the controls. Keep in mind that that the report definitions are a reflection of the report design, so specific reference should be made to controls within the header, group headers and footers, detail sections, etc.
I am sorry I dont have sample code to offer with me, perhaps someone can provide or add more clarity to what I have presented.
Hope this is of some help.
Regards,
John W.