What is RPG 3 and Why You Need It for Your Business
RPG 3 is a dialect of the RPG programming language that was first announced with the IBM System/38 in 1978. RPG stands for Report Program Generator, and it was originally designed to create reports from data stored in databases. However, over the years, RPG has evolved into a general-purpose programming language that can handle various tasks such as data processing, business logic, user interface, web services, and more.
RPG 3 is one of the versions of RPG that was developed for the IBM i platform, formerly known as AS/400 or iSeries. IBM i is a family of integrated operating systems that run on IBM Power Systems servers. IBM i offers a robust and secure environment for business applications, with built-in features such as database management, security, backup, and recovery. IBM i also supports multiple programming languages, such as RPG, COBOL, CL, Java, C#, PHP, and Python.
Some of the main features of RPG 3 are:
It uses external file descriptions, which means that disk files are built and RPG 3 programs are attached to them at compile time.
It uses display formats to describe the fields displayed and received by the RPG 3 WORKSTN file. These specifications are also external in nature and must be compiled before the RPG 3 program.
It uses operation codes to perform various actions on data, such as calculations, comparisons, assignments, branching, looping, input/output, etc.
It supports cycle programming, which is a method of processing records in a file sequentially until the end-of-file condition is reached.
It supports subprocedure logic, which allows the programmer to define reusable blocks of code that can be called from other parts of the program.
It supports indicators, which are binary variables that can be used to control the flow of logic or the display of fields.
Example of an RPG 3 program
In this section, I will show you how to create and compile an RPG 3 program using two different methods: RDi (Rational Developer for i) or PDM (Program Development Manager) and SEU (Source Entry Utility). RDi is an integrated development environment (IDE) that provides various tools for editing, compiling, debugging, and testing RPG programs. PDM and SEU are older tools that run on a green-screen interface and allow the programmer to create and manage source members.
The example program that I will write is a simple one that calculates the factorial of a number. The factorial of a number n is defined as the product of all positive integers less than or equal to n. For example, the factorial of 5 is 5 x 4 x 3 x 2 x 1 = 120. The program will prompt the user to enter a number between 1 and 10, then display the result on the screen.
To create an RPG 3 program using RDi, follow these steps:
Create a connection to your IBM i system. You will need to provide your system name, user ID, password, and port number. You can also specify other connection settings, such as SSL, proxy, and filters.
Create a source physical file (PF-SRC) on your IBM i system. This is a file that contains the source code of your RPG 3 program. You can use the CRTSRCPF command to create a PF-SRC, or you can use the RDi wizard to create one.
Create a source member within the PF-SRC. This is a logical unit that stores the actual source code of your RPG 3 program. You can use the ADDPFM command to create a source member, or you can use the RDi wizard to create one. You will need to specify the member name, type (RPG for RPG 3), and text description.
Open the source member in the RDi editor. You can use the Remote Systems Explorer view to navigate to your PF-SRC and source member, then double-click on it to open it in the editor. You will see a blank screen with a line number column on the left.
Write your RPG 3 program in the editor. You will need to follow the RPG 3 syntax and specifications, which are explained in detail in the IBM Knowledge Center. You can also use the RDi features such as content assist, syntax checking, code formatting, and code templates to help you write your program faster and easier.
Save and compile your RPG 3 program. You can use the Ctrl+S shortcut to save your source member, then right-click on it and select Compile > Compile Current Member to compile it. You will see a message window that shows the status and results of the compilation. If there are no errors, you will see a message that says "Compile completed successfully".
Run and test your RPG 3 program. You can use the Run > Run As > IBM i PGM/CL Command option to run your program on your IBM i system. You will see a console window that shows the output of your program. You can also use the Debug > Debug As > IBM i PGM/CL Command option to debug your program step by step using breakpoints, watches, and expressions.
Using PDM and SEU
To create an RPG 3 program using PDM and SEU, follow these steps:
Sign on to your IBM i system using a terminal emulator such as TN5250 or PuTTY. You will need to provide your user ID and password.
Create a library on your IBM i system. This is a container that holds various objects such as files, programs, commands, etc. You can use the CRTLIB command to create a library, or you can use an existing library that you have access to.
Create a source physical file (PF-SRC) within the library. This is a file that contains the source code of your RPG 3 program. You can use the CRTSRCPF command to create a PF-SRC, or you can use an existing PF-SRC that you have access to.
Create a source member within the PF-SRC. This is a logical unit that stores the actual source code of your RPG 3 program. You can use the ADDPFM command to create a source member, or you can use an existing source member that is empty or has no code in it. You will need to specify the member name, type (RPG for RPG 3), and text description.
Open the source member in SEU. SEU is a text editor that runs on a green-screen interface and allows you to edit source members. You can use the STRSEU command to start SEU and open your source member. You will see a screen with a header that shows the member name, type, and description, and a body that shows the source code lines with line numbers on the left.
Write your RPG 3 program in SEU. You will need to follow the RPG 3 syntax and specifications, which are explained in detail in the IBM Knowledge Center. You can also use some SEU features such as prompting (F4), copying (F15), moving (F16), deleting (F17), inserting (F18), finding (F19), changing (F20), and verifying (F21) to help you write your program faster and easier.
Save and compile your RPG 3 program. You can use the F2 key to save your source member, then press F3 to exit SEU. Then you can use the CRTBNDRPG command to compile your program. You will see a message window that shows the status and results of the compilation. If there are no errors, you will see a message that says "Program created successfully".
Run and test your RPG 3 program. You can use the CALL command to run your program on your IBM i system. You will see a screen that shows the output of your program. You can also use the STRDBG command to debug your program step by step using breakpoints, watches, and expressions.
Advantages and disadvantages of RPG 3
RPG 3 is a language that has been used for decades by many IBM i developers to create various applications for business and industry. It has some advantages and disadvantages that you should be aware of before deciding to use it for your projects.
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Advantages of RPG 3
Some of the benefits of using RPG 3 are:
It is a mature and stable language that has been tested and proven over time.
It is easy to learn and use, especially for programmers who are familiar with the IBM i environment and database.
It is efficient and fast, as it can process large amounts of data quickly and accurately.
It is compatible and portable, as it can run on any IBM i system without requiring any changes or modifications.
It is supported and maintained by IBM, as well as by various third-party vendors and communities that offer tools, libraries, frameworks, and services for RPG 3 development.
Disadvantages of RPG 3
Some of the limitations and challenges of using RP