The logic cycle is the backbone of the RPG programming language. Perhaps it's use has faded in recent years but it can still be used as effectively in RPGLE as it could in RPG2.

Tthe first and last time the program goes through the cycle is slightly different from all the in-between cycle runs:

Before the first record is read the first time through the cycle, the program resolves any parameters passed to it, writes the records conditioned by the First Page (1P) indicator, does file and data initialization, and processes any heading or detail output operations. This may also include printing heading lines.

 Expandable subfiles in RPGLE

An expandable subfile is one in which ideally one page of records are loaded at a time. Subsequent pages are added to the subfile as per the user demand.

In the expandable subfile the subfile size must be atleast one greater than the page size.

The ILE RPG program to process an expandable subfile has typically the following flow

 So far we have dealt with display only subfiles. Now we will learn the subfiles which can accept user input and process it.

Generally the following are the steps in which we can display and process an input capable subfile. The editable subfiles are very much similar to the display-only subfiles except the last two steps where these subfiles are read (USING READC Or CHAIN) and updated (Using UPDATE). The steps to process an editable subfile in RPG IV are as given below.

Free Tutorial on AS400 Subfiles in ILE RPG (RPG-IV)

After learning the basic concepts of ILE RPG IV an RPG programmer's next stop is Subfiles. AS/400 Subfiles should always be learnt after one has acquired basic skills of RPG IV. One should be able to understand the basic RPG IV concepts like Processing display files, Record Formats, Physical Files, Logical Files, How to interact with database files and finally how to process an interactive display file. 

Introduction to subfiles

Basically subfiles are display-file-concept. Whenever we have to display some tabular data we have two options

# Define as many required fields

RPG and the AS/400 platform have a long history.

When the System/3 was introduced in the 1970s, RPG was first released , the language evolved and RPG II use of the logic cycle was many programmers first experience of pullng hair out while staring at a green screen. RPG III was released with the System/38, which included the ability to work with a fully integrated database. In 1994, RPG IV was released, with it's ILE abilities. Now referred to as RPGLE the language is evolving with every release of i5/OS (the IBM operating system).