Using a variable to index an array of strings?

I have a variable IDX that varies from 0-10, can I use the following:

CONCAT ArrayStr[IDX] ArrayStr[5] Destination

To write to a string destination? I'm using ladder diagrams and it's showing "??" under Source A where I'm using IDX to call for a string, and showing the correct 'string' under Source B where I'm calling the 5th member of ArrayStr.

Yep, that's fine - since IDX is variable, RSLogix5000 doesn't display the associated string, even though it probably could....