HP HP-32S - Loops (GTO, LOOP)

Itis good practice in a program to make sure that any conditions you
will be testing start outina known state. Current flag settings depend
on how they have been leftby earlier programs that have been run.
You should not assume that any given flag is clear, for instance, and
that it willbe set only if something in the program setsit. You should
make sure of this by clearing the flag before the condition arises that
might set it. See the example below.
Example: Using Flags. The "Quadratic Equation" program on page
191 in part 4 uses flag 0 in conjunction withthe x <©? comparison to
remember the signof B. Note that line Qll clears flag 0 to makesure
that it will be set for only the condition desired.
Qll CF 0 Makes sure that flag 0 is clear.
Q12x<0? IsB(in X-register) negative?
Q13 SF 0 Sets flag 0 if B is negative.
Q23 FS? 0 Is flag 0 set (is B negative)?
Q24 +•- If yes, change sign.
Q25 + In either case, add.
Other programs in part 4 that make use of flags are "Curve Fitting"
and "UnitConversions." Theyboth use flags to remember which con
dition the user wants solved (which type of curve, which type of
conversion), thereby affecting which options or calculations are
chosen.
Loops (GTO, LOOP)
Branching backwards—that is, to a labelin a previous line—makes it
possible to execute part of a program more than once. This is called
looping.
6: Programming Techniques 99