The fact that the Goto operation is not supported in free-format should not be a problem for most programmers, since good programming practice should have precluded its use long ago. But we all have coded--or at least seen--Goto loops, such as the following:
C Exfmt Scrnfmt
C If *In03 = *Off and *In12 = *Off
C* Not exit and not cancel, so process data from the screen
C If Error_1
C Eval *In20 = *on
C Goto Loop
C Endif
C If Error_2
C Eval *In21 = *On
C Goto Loop
C Endif
C
C* More error checking and looping back...
C* Error messages on the screen are conditioned by *In20, *In21, etc.
How could the above be coded without Goto? The following is a fixed-format scheme:
C Exfmt Scrnfmt
C If *In03 = *Off and *In12 = *Off
C* Not exit and not cancel, so process data from the screen
C If Error_1
C Eval *In20 = *on
C Iter
C Endif
C If Error_2
C *In21 = *On
C Iter
C Endif
Here's the free-format alternative:
Dou Exit or Cancel; // Begin screen display and edit
Exfmt Scrnfmt; // Display the screen
If Not Exit and Not Cancel; // Check for F3 or F12 keys
If Error_1; // Checking for error 1
Scrnfield1_error = *On; // Set error flag indicator
Iter; // Exit remaining check section
Endif;
If Error_2; // Checking for Error 2
Scrnfield2_error = *On; // Set error flag indicator
Iter; // Exit remaining check section
Endif;
//
// More error checking here
//
Enddo;
/end-free
The free-format alternative is very much the same as a good fixed-format alternative. The only difference is that I have chosen to use named indicators from the display file instead of numbered ones. This is not required, but it sure adds a lot of clarity to the code. Don't forget to use the file-level keyword INDARA in the DDS of the display file if you choose to use a named indicator data structure. Also, when doing this, the numbered indicators in the RPG program no longer reference the display file indicators. They can only be referenced by their name. (For more information on named file indicators, check for indicator data structures in the RPG Reference manual. Look at page 133 for information and page 142 for an example.)
Other logical flow operators that are missing in free-format are DO and case (CASxx). The DO operation is easily replaced by the FOR operation. The following shows a DO group with a starting value other than one, an increment other than one, and the index option:
C Eval Array(Index) = Index;
C Index Chain SubfileRec
C If %found
C Eval SF_Field_1 = 44
C Endif
C Enddo 2
Here's the free-format equivalent:
For Index = 2 to 20 by 2; // Set up a controlled loop
Array(Index) = Index; // Set Array element
Chain Index SubfileRec; // Get subfile record
If %found; // If found
SF_Field_1 = 44; // Set subfile field
Endif;
Endfor;
/End-free
Case groups can easily be modified to use the Select, When, and Other operations.
The If, DOW (Do While), and DOU (Do Until) operations are still available in free-format. And the logic interrupters Iter (Iteration), Leave (leave Do or For group), and LeaveSR (leave subroutine) are an essential part of your logical structures. Also, the new operation ElseIf could be a very nice option in a program, eliminating a long string of Endifs.
Coding in free-format RPG IV is not a panacea for programmers, but it does force us into using better program structures. By using indenting, named indicators, indicator data structures for files, and line comments, program maintenance productivity and overall readability is greatly improved.
Jim Martin is the corporate technical instructor at Jack Henry & Associates in Monett, Missouri. He is a veteran of RPG programming, beginning in 1967 with a position at IBM as a systems engineer. Later, he was a staff programmer at the Rochester systems programming lab. For eight years, he was at Lakeview Technology as an AS/400 and RPG instructor and a speaker at various local midrange user group meetings and conferences. He can be reached by email at
Jim Martin holds a BS degree in mathematics and an MS in computer science. For 26 years, he was employed by IBM, where he wrote RPG applications for customers and worked in the programming laboratory as a programmer on portions of CPF and the OS/400 operating system. After leaving IBM, Jim took post-graduate work in computer science and performed RPG training. He is an IBM-certified RPG IV developer and author of multiple bestselling editions of Free-Format RPG IV, which, since the book's initial publication in 2005, have taught thousands of RPG IV programmers how to be successful with the free-format coding style.
MC Press books written by Jim Martin available now on the MC Press Bookstore.
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