you need to cycle through the array that holds the values.
if you are displaying them, you will probably want a stringvar and to loop (CR help for syntax)....probably a FOR loop where the upper limit is found by UPPER({?parameter})-1 (the array starts at index [0] I am pretty sure...again CR help can guide you)
Obviously in your loop you will want to concatenate the values together.
if you just need to see if a value has been selected, then you will be using the 'IN' command....again CR help, look at arrays or IN, either should give you examples of how to proceed.
HTH