HP HP-28S - Asking for a Choice

The displayed menu shows the labels [:::I!:::] , [=:I::=:J, and :::::::::r::::::::I,
which resemble labels in the Solver menu. After entering a value on
the stack, the user can simply press one of these keys to store the
value in the corresponding variable. After entering the values, the
user must press .1 caNT I to continue program execution.
Asking for a Choice
For complex tasks it's best to write a series of small programs, each
performing a small task. In some cases the user has several options
for performing one of the tasks. One approach is to write alternative
programs to perform that task.
Assume that one task is completed, and the user must choose among
the programs HOP, SKIP, and JUMP for the next task. The following
sequence creates a custom user menu for programs HOP, SKIP, and
JUMP, sounds a tone to alert the user, and ends program execution .
... { HOP SK I P ,..IUt'1P } MEtW 440 ,1 BEEP ~:.
The displayed menu shows the labels HOP , SK I P ,and JUMP ,
which resemble labels in the User menu. When the user presses one
of the menu keys, the next task is performed. That task may end with
a similar sequence, offering the user a different set of options; and so
on throughout the entire complex task.
A More Complicated Example
The example below displays a message, waits until the user presses a
key,
and checks that the key is defined (that is, represents one of the
choices). If the key is defined, the corresponding action is performed;
if the key isn't defined, an error message is displayed and the process
starts over.
This example uses
program structures described in the previous chap-
ter. There is an "outer" DO ... UNTIL ... END structure that repeats
until the user presses a defined key. The outer DO clause contains an
"inner" DO ... UNTIL ... END structure that repeats until the user
presses a key. The outer UNTIL clause contains a conditional that
27: Interactive Programs 235