You want the subreport to use a value in the main report, or a parameter from the main report? Your post title references a parameter, your post does not. Perhaps you're unfamiliar with Crystal syntax, but these are very different things.
Your description leaves far too much to the imagination, try posting technical onformation:
Database/connectivity used
Example dtaa
Expected output
A parameter can be linked to a subreport field by right clicking the subreport and select change subreport links, then selecting the parameter from the main report, and the field in the subreport.
If you have a value in the main report which is to be linked to a subreport, group on the field and then link via that field.
If you need to return a value from a main report to a subreport, or vice verssa, use shared variables, as in:
mainreport formula:
whileprintingrecords;
Shared Numbervar MyValue:= {table.field};
As long as this formula is before the subreport executes, you can reference it, as in:
whileprintingrecords;
Shared Numbervar MyValue;
MyValue/{subtable.field}
You may have the architecture backwards and want the subreport as the main report, but it's hard to say from your post. A little effort on your part will minimize the requirement for us to cover all possibilities and result in faster, accurate responses.
Hope this helps.
-k
