Depending on what you use the parameter for in the subreport, you may be able to use a formula instead of the parameter.  You can use code to put a value into the formula almost the same way that you do the parameter.

I am new to Crystal report. I am having a main report with summary information and two subreports with different details information. I have already created a prompt call ?site_id in the main report and sub_siteID for subreport.
When I run the main report, prompt will ask to enter the site_id for main report, but when I run the subreport, the prompt will ask again to enter the site id which I don't want to (avoid the mistake and repeat work).
How can I make the report that will prompt once only for the siteID?

Appreciate your help. Thanks