IBM TSO/E REXX User Manual

Exercise - Using a DO WHILE Loop
Write an exec with a DO WHILE loop that asks passengers on a commuter airline if
they want a window seat and keeps track of their responses. The flight has 8
passengers and 4 window seats. Discontinue the loop when all the window seats
are taken. After the loop ends, display the number of window seats taken and the
number of passengers questioned.
ANSWER
Possible Solution
/******************************** REXX *****************************/
/* This exec uses a DO WHILE loop to keep track of window seats in */
/* an 8-seat commuter airline. */
/*******************************************************************/
window_seats = 0 /* Initialize window seats to 0 */
passenger = 0 /* Initialize passengers to 0 */
DO WHILE (passenger < 8) & (window_seats \= 4)
/****************************************************************/
/* Continue while you have not questioned all 8 passengers and */
/* while all the window seats are not taken. */
/****************************************************************/
SAY 'Do you want a window seat? Please answer Y or N.'
PULL answer
passenger = passenger + 1
/* Increase the number of passengers by 1 */
IF answer = 'Y' THEN
window_seats = window_seats + 1
/* Increase the number of window seats by 1 */
ELSE NOP
END
SAY window_seats 'window seats were assigned.'
SAY passenger 'passengers were questioned.'
DO UNTIL Loops
DO UNTIL loops in a flowchart appear as follows:
As REXX instructions, the flowchart example looks like:
DO UNTIL
instruction(s)
expression
False
True
END
Using Looping Instructions
Chapter 4. Controlling the Flow Within an Exec 53

IBM TSO/E REXX Specifications

General

Brand	IBM
Model	TSO/E REXX
Category	Computer Hardware
Language	English

Summary

Part 1. Learning the REXX Language

Chapter 1. Introduction

Explains the REXX programming language, its features, and suitability for various users.

Chapter 2. Writing and Running a REXX Exec

Details the process of writing, running, and understanding REXX execs, including syntax rules and common issues.

Chapter 3. Using Variables and Expressions

Covers REXX variables, expressions, operators, and tracing techniques for data manipulation and calculations.

Chapter 4. Controlling the Flow Within an Exec

Explains how to alter REXX exec execution using conditional, looping, and interrupt instructions.

Chapter 5. Using Functions

Describes REXX functions, including built-in, user-written, and packages, and how to use them.

Chapter 6. Writing Subroutines and Functions

Guides on writing, calling, and passing information to REXX subroutines and functions.

Chapter 7. Manipulating Data

Covers REXX data manipulation using compound variables, stems, and various parsing techniques.

Part 2. Using REXX

Chapter 8. Entering Commands from an Exec

Explains how REXX execs can interact with the operating system by issuing TSO/E and host commands.

Chapter 9. Diagnosing Problems Within an Exec

Details techniques for diagnosing and debugging REXX execs using tracing and special variables.

Chapter 10. Using TSO/E External Functions

Describes TSO/E external functions available for interacting with the system and performing specific tasks.

Chapter 11. Storing Information in the Data Stack

Explains how to use the REXX data stack for temporary storage, passing information, and managing buffers.

Chapter 12. Processing Data and Input/Output Processing

Covers dynamic REXX expression modification and processing data to/from data sets using EXECIO.

Chapter 13. Using REXX in TSO/E and Other MVS Address Spaces

Explains how to run REXX execs in TSO/E and non-TSO/E MVS address spaces and available services.

Part 3. Appendixes

Appendix A. Allocating Data Sets

Guides on creating and allocating data sets, including checklists for ISPF/PDF and ALLOCATE commands.

Appendix B. Specifying Alternate Libraries with the ALTLIB Command

Details using the ALTLIB command to specify and manage alternative libraries for implicit execution.

Appendix C. Comparisons Between CLIST and REXX

Compares REXX and CLIST languages, highlighting similarities and differences in features and capabilities.

Appendix D. Notices

Provides legal notices, warranty disclaimers, copyright, and trademark information.

Bibliography

TSO/E Publications

Lists IBM publications related to TSO/E, including administration, CLISTs, and general information.

Related Publications

Lists IBM publications related to z/OS MVS and ISPF, covering system programming and administration.

Index