HP HP-28S User Manual

IF ... THEN ... END
If an ELSE clause isn't required-that is, if the choices are to do
something or do nothing-you can omit ELSE from the program
structure. The following example ensures that the object in level 1 is
greater than the object in level 2 by swapping them if necessary.
IF DUP2 , THEN SWAP END
Note the use of DUP2 to make copies of the objects. The copies are
then consumed by the comparison ,. For another example of IF
THEN ... END, see "SORT (Sort a List)" on page 270.
1FT (If-Then-End Command)
You could write the previous example by using the command 1FT in-
stead of the program structure:
DUP2 , « SWAP» 1FT
The sequence D U P 2 'leaves a flag on the stack, the program
.,=,: ::;;(.j A P :,=,. goes on the stack, and the command 1FT takes the flag
and the program as arguments. If the flag is true, 1FT evaluates the
program; if the flag is false, 1FT drops the program. The result is iden-
tical to the program-structure form.
Error Traps
In some cases you can predict that an error might occur during pro-
gram execution. Normally an error cancels program execution; but if
you
trap the offending command by enclosing it in a special program
structure, the program can continue execution when the error occurs.
Remember the problem with (sin x)/x-it causes an Infinite Result er-
ror
when x = O. Another method for defining (sin 0)/0 = 1 would
be:
IFERR X SIN X / THEN DROP2 1 END
26: Program Structures 227

HP HP-28S Specifications

General

Introduced	1988
Memory	32 KB
Number of Digits	12
Type	Scientific Calculator
Manufacturer	Hewlett-Packard (HP)
Display	LCD
Processor	Saturn
Programming	RPL

Summary

HP-28S Advanced Scientific Calculator Owner's Manual

Part 1: Fundamentals

Introduces basic operations, calculator features, and core concepts.

Getting Started

Covers initial setup, basic operations, and calculator overview.

Doing Arithmetic

Explains methods for performing calculations using stack and expressions.

Part 2: Summary of Calculator Features

Objects

Describes fundamental data types, symbolic operations, and programming elements.

The Command Line

Explains input methods, cursor control, and command entry.

The Stack

Reviews stack concepts and commands for manipulating objects.

Part 3: Programming

Program Structures

Covers conditional logic, loops, and error handling in programs.

Conditional Structures

Explains testing conditions and making decisions within programs.

Definite Loop Structures

Details structures for executing code a specific number of times.

Appendixes & Indexes

Appendix A: Assistance, Batteries, and Service

Provides troubleshooting, battery info, and service details.

Answers to Common Questions

Addresses frequent user queries and common calculator issues.

Appendix B: Notes for HP RPN Calculator Users

Highlights differences for users familiar with RPN calculators.

Appendix D: Menu Map

Lists commands by menu, with descriptions and page references.

Contacting Hewlett-Packard