Crystal Reports : Providing Custom Parameter Choices

Let us consider our {?UserID} parameter, which accepts multiple values.
Let us further consider that the end-user will need to occasionally print the report for all UserID's. They could simply add each UserID to the parameter before printing the report, but in cases of many UserID's, this becomes cumbersome.
A better solution is to give an "all" option in the parameter choices, then use the following code:

if {?UserID} not like "*all*" then {SALES.USERID} = {?UserID} else true

Here is what's happening:
IF our parameter DOES NOT have he word "all" within it, we execute the Selection Criteria normally. The trick here is that our ELSE clause ends in TRUE, which means that we "skip over" this part of the Selection Criteria, therefore returning ALL UserID's.