HP HP-28S - Page 253

Look at the general rules at the beginning of this section. Now you
can choose one of the three alternatives described in step 4.
For this example, press SST repeatedly until the 0 annunciator dis-
appears, indicating that FIB2 is completed. (These single-steps not
shown here.)
The calculation for F} executes only the THEN clause in FIB2.
For
the second example, execute 3 F I 82 and single-step through
the calculation for F
3
.
This executes the ELSE clause, including the
START ... NEXT loop. You'll see that, for n = 3, the START ...
NEXT loop is executed twice.
For
the third example, suppose you want to single-step the START ...
NEXT loop as a whole-seeing the stack before each iteration of the
loop, but not single-stepping all the steps in FIB2 or in the loop itself.
To do so, move the HALT command inside the loop. Then FIB2 won't
halt until it reaches the loop, and you can use .1 CO NT I (continue) to
execute
the loop one iteration at a time.
Use VISIT to
return FIB2 to the command line.
I USER I
~ FIB2 .1 VISIT I
• HALT "* n
«
IF n 1 f
THEN n
Use the cursor menu keys to delete HALT. Then insert HALT as
shown (following the START command).
Store the edited version of FIB2.
I ENTER I
IF n 1 f
THEN n
ELSE 0 1 2 n
START HALT .DUP Roo.
Start the calculation for F
3
.
FIB2 will halt before performing the loop.
3 FI82 IL ____ .JI
252 28: Programming Examples