Detect number entry on HP-35s?

[mbrethen]

The idea is to fill a number of unnamed indirect variables and then branch off (terminate loop) when the user does not enter a value, similar to using FC?C 22 on the 41c.

Here is the beginning of my code:

Code:

W001  SF 0
W002  STO I
W003  1.001
W004  STOx I
W005  ENTER
W006  FP
W007  1E3
W008  x
W009  ENTER
W010  CLx
W011  [INTG(LASTx),REGY]
W012  PSE
W013  R^
W014  R^
W015  INPUT A
W016  (TEST ENTRY)
W017  GTO WYYY
W018  STO (I)
(CODE)
WXXX  GTO W005
(CODE)
WYYY

The user inputs the starting register before executing. I could require the user to also input the total entries, but it would be nice if the program could figure that out ;-)