Hmmm... given the constraint iNumber can only be 1-31, you could also make it more straightforward:

FUNCTION fOrdinal( iNumber )
return subs("stndrdthththththththththththththththththstndrdthththththththst", (iNumber*2)-1, 2)

>>parameter x
>>return iif(between(x, 11, 13), "th", iif(right(str(X),1) = "1", "st", iif(right(str(X),1) = "2", "nd", iif(right(str(X),1) = "3", "rd", "th"))))

---

Ken, I spotted your one-liner and felt compelled to match it ;-)

FOR iNumber = 1 TO 31
>   ? "  " + TRANSFORM( iNumber ) + fOrdinal( iNumber )
>NEXT iNumber
>
>****************************
>FUNCTION fOrdinal( iNumber )
>****************************
>   RETURN IIF( NOT BETWEEN( iNumber, 11, 13 ) AND BETWEEN( MOD(iNumber,10), 1, 3 ) ;
>             , SUBSTR( "stndrd", (MOD(iNumber,10) * 2) -1, 2 ) ;
>             , "th" )