HP HP-32S - Page 80

Press IR/SI (run/stop) or a to resume the program. The value you
keyed in then writes over the contents of the X-register and is stored
in the given variable. If you have not changed the displayed value,
then that value is retained in the X-register.
The area-of-a-circle program with an INPUT instruction looks like
this:
R01 LBL R
fl02 INPUT R
R03 x*
R04 tf
R05 x
R06 RTN
Using INPUT in a Program.
1. Decide which data values you will need, and assign them names.
(In the area-of-a-circle example, the onlyinput needed is the ra
dius, which we can assign to R.)
2. In the beginningof the program, insert an INPUT instruction for
each variable whose value you will need. Later in the program,
when you write the part of the calculation that needs a given
value, insert a I RCL I variable instruction to bring that value back
into the stack.*
For Example: See theTime Value of Money* program on page 222
in part 4. The first thing that routine T does is collect all the necessary
input for the variables N, I, B, P, and F (lines T02 through T06).
• Since the INPUT instruction also leaves the value you just entered in the X-register, you
don't have to recall the variable ata later time—you could INPUT it and use it when you
need it. You might be able to save some memory space this way. However, ina long pro
gram it is simpler to justinput all your data up front, andthen recall individual variables as
you need them.
Remember also matthe user of the program can do calculations while the program is
stopped, waiting for input. This can alter the contents of the stack, which might affect the
next calculation to be doneby the program. Thusthe program should not assume that the
X-, Y-, and Z-registers'contents will be the same before and after the INPUT instruction. If
you collect allthe data in the beginning andthen recall them whenneeded for calculation,
then this prevents the stack's contents from being altered just before a calculation.
78 5: Simple Programming