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RPG IV Overview
Chapter 1. Overview of the RPG IV Programming Language
This chapter presents a high-level review of the features of the RPG IV program-
ming language that distinguish RPG from other programming languages. You
should be familiar and comfortable with all of these features before you program in
the RPG IV language. The features discussed here encompass the following
subjects:
Coding specifications
The program cycle
Indicators
Operation codes
For more information on RPG IV, see the
ILE RPG for AS/400 Reference
.
RPG IV Specifications
RPG code is written on a variety of specification forms, each with a specific set of
functions. Many of the entries which make up a specification type are position-
dependent. Each entry must start in a specific position depending on the type of
entry and the type of specification.
There are seven types of RPG IV specifications. Each specification type is optional.
Specifications must be entered into your source program in the order shown below.
Main source section:
1. Control specifications provide the compiler with information about generating
and running programs, such as the program name, date format, and use of
alternate collating sequence or file translation.
2. File description specifications describe all the files that your program uses.
3. Definition specifications describe the data used by the program.
4. Input specifications describe the input records and fields used by the
program.
5. Calculation specifications describe the calculations done on the data and the
order of the calculations. Calculation specifications also control certain input
and output operations.
6. Output specifications describe the output records and fields used by the
program.
Subprocedure section:
1. Procedure specifications mark the beginning and end of the subprocedure,
indicate the subprocedure name, and whether it is exported.
2. Definition specifications describe the local data used by the subprocedure.
3. Calculation specifications describe the calculations done on both the global
and local data and the order of the calculations.
Copyright IBM Corp. 1994, 1999 3