D cvtZonedToInt pr 10i 0 extproc('QXXZTOI')
d cvtZone * value options(*string)
d cvtDigits 10i 0 value
d cvtFraction 10i 0 value
You should remove 'options(*string)' from the first parameter. The input isn't a string, it's a zoned decimal number.
I have no idea why you'd want to use this for your purposes, though. Is your goal really to convert zoned decimal to integer? And if it is, why use a C function? Why not use %int()?
AFIAK, your issue is thast you have bytes in zoned decimal format, but they've been stored (for some weird unknown reason) in an alphanumeric field instead of in a zoned decimal field.
The solution to that is to use overlaid fields in a data structure. Though, you can solve the same problem by passing a mismatched parameter (which is what you've done by calling QXXZTOI) or by pointer logic.
But, an overlaid data structure field would perform a lot better than calling this API, and it'd also make a lot more sense to the next guy reading your program.