You're asking about the evolution of RPG, and it's a good question because the distinctions can be a bit confusing! Here's a breakdown of RPG III, RPG IV, and RPG Free Format:
RPG III
- The Bridge: RPG III was a significant step up from the very early RPG versions. It introduced structured programming concepts (like
IF-THEN-ELSE and DO loops), subroutines, and better data handling. This made RPG more powerful and flexible.
- Still Column-Bound: However, RPG III still relied on a rigid, column-oriented syntax. You had to write code in specific columns on the screen, which could be cumbersome.
- Legacy: You'll likely encounter RPG III programs if you work with older IBM i (AS400) systems. It's important to understand it for maintenance, but it's not used for new development.
RPG IV
- Modernization: RPG IV (also known as ILE RPG) is the current, widely used version. It brought major changes:
- Integrated Language Environment (ILE): This is a big deal! It allows RPG programs to work seamlessly with other ILE languages like COBOL and C. This enables code sharing and modular development.
- Free-form Syntax: RPG IV introduced the option of free-form syntax, which we'll talk about more in a moment.
- Enhanced Features: RPG IV has grown over the years with lots of improvements: data structures, subprocedures, better file handling, and more.
RPG Free Format
- A Style within RPG IV: This is where the confusion often comes in. RPG Free Format is not a separate version of RPG. It's a coding style within RPG IV.
- Flexibility: Free-form syntax lets you write RPG code in a more modern, less restrictive way. You're not tied to specific columns anymore. It's much more like languages you might be familiar with (C#, Python, etc.).
- The Standard: For new RPG IV development, free-form is the preferred style. It makes code easier to read, write, and maintain.
Here's a table to summarize:
