109 IBM RPG interview questions to hire top developers

IBM RPG remains relevant in numerous enterprises, particularly those leveraging the IBM i platform; thus, hiring the right talent is important. Ensuring you ask the right questions can help you filter out candidates who lack the skills to develop, maintain, and modernize RPG applications effectively.

This blog post provides a curated list of IBM RPG interview questions, categorized by experience level from freshers to experienced professionals, including multiple-choice questions (MCQs). You'll find targeted questions for assessing a candidate's knowledge across different stages of their career.

By utilizing these questions, you can evaluate candidates' skills and ensure they are a great fit for your team, and consider using an IBM DB2 online test to streamline your screening process before the interviews.

Table of contents

IBM RPG interview questions for freshers

1. What is RPG in IBM i, and why is it important for business applications?

RPG (Report Program Generator) is a high-level programming language originally developed by IBM. On the IBM i (formerly AS/400) platform, it's a primary language for developing business applications. It has evolved significantly over the years, from RPG II to RPG IV (also known as ILE RPG or RPGLE), incorporating modern programming concepts and features.

RPG's importance stems from its strong integration with the IBM i operating system and database (Db2 for i). It's highly efficient for data processing, report generation, and business logic implementation. Many mission-critical applications in finance, manufacturing, and distribution rely on RPG due to its stability, reliability, and performance. Also, huge code base exists in RPG. So, modernizing RPG applications is still relevant.

2. Can you explain the basic structure of an RPG program?

RPG programs typically consist of three main parts: the header specifications, input specifications, calculation specifications, and output specifications. The header specifies the program type and compiler options. Input specifications define the data structures read from files or devices, including field names, data types, and record formats.

The calculation specifications are where the main logic resides. They use operations like ADD, SUB, MOVE, and IF to manipulate data, call subroutines, and perform calculations. This is usually done via C specs. Finally, output specifications describe how data is written to files, printers, or displays. They define the layout, field positions, and formatting options for output records. Modern RPGLE often also contains free-form logic using /FREE and /END-FREE directives. These often replace the C specs with more structured programming concepts.

3. What are the different data types available in RPG?

RPG provides a variety of data types to represent different kinds of data. Some of the most common include:

• Character: A - Used for storing character strings. Can be fixed or variable length.
• Numeric:
  • Integer: I - Signed integer values.
  • Unsigned Integer: U - Unsigned integer values.
  • Packed Decimal: P - Stores numbers in a packed decimal format for efficient storage.
  • Zoned Decimal: S - Stores numbers in a zoned decimal format.
  • Float: F - Floating-point numbers for representing real numbers with fractional parts.
• Logical: N - Represents boolean values (true or false), stored as '1' or '0'.
• Date: D - Represents dates.
• Time: T - Represents times.
• Timestamp: Z - Represents a combination of date and time.
• Object: O - Represents a pointer to an object.
• Pointer: * - Used to store the address of another variable or data structure. Includes both basing pointers and procedure pointers.
• Data Structure: DS - A composite data type that groups related data elements together. Can contain other data types, including other data structures.

4. Explain what a 'fixed-form' RPG is.

A 'fixed-form' RPG, also sometimes referred to as a 'linear' RPG, describes a game where the story and progression are largely predetermined. The player has limited ability to significantly alter the main storyline or the ending. While there may be some side quests or minor choices, the core narrative path is generally set. Think of it as reading a book where you can choose some footnotes (side quests), but the main story unfolds in a specific, pre-defined way regardless of your minor choices.

In contrast to open-world or sandbox RPGs that emphasize player agency and emergent narratives, fixed-form RPGs prioritize a carefully crafted and directed storytelling experience. The focus is often on character development within the context of the fixed narrative, rather than on world exploration or altering the course of the story itself.

5. What's the difference between 'free-form' RPG and 'fixed-form' RPG?

The primary difference lies in the structure and constraints imposed on the game's narrative and player actions. A 'fixed-form' RPG, also sometimes referred to as a 'linear' RPG, presents a tightly controlled story with predetermined paths and limited player agency. The game dictates where the player can go, what quests they must complete, and often how they must complete them. Think of older JRPGs or some story-driven action-adventure games where the narrative is paramount. In contrast, a 'free-form' RPG, often called a 'sandbox' or 'open-world' RPG, offers a much more open-ended experience. Players have significant freedom to explore the game world, pursue quests in any order, and make choices that genuinely impact the story and the world around them. Examples include games like The Elder Scrolls series or tabletop RPGs where the Game Master adapts to player actions.

Essentially, 'fixed-form' RPGs emphasize a pre-defined narrative experience, while 'free-form' RPGs prioritize player freedom and emergent storytelling.

6. How do you declare a variable in RPG?

In RPG (Report Program Generator), you declare variables using the D-spec (Definition Specification). The D-spec is used to define various data elements, including variables, constants, and data structures. The general format involves specifying the variable name, data type, length, and other attributes.

For example, a simple integer variable named myInteger with a length of 5 and zero decimal positions would be declared as follows in fixed-form RPG:

rpgle D myInteger S 5 0

In free-form RPG, you would use the DCL-S keyword:

rpgle DCL-S myInteger INT(5);

7. How do you use comments in an RPG program?

In RPG (Report Program Generator), comments are crucial for explaining code logic and improving readability. There are a few ways to use comments:

• * in Column 7: Any line with an asterisk (*) in column 7 is treated as a full-line comment. This is the most common way to add comments.
• //: The double slash (//) indicates a free-form comment. Everything after // on the same line is ignored by the compiler.
• /* ... */: The /* and */ delimiters allow for multi-line comments or inline comments. Anything between /* and */ is considered a comment.

For example:

* This is a full-line comment
C                   EVAL      Result = Value1 + Value2  // Add the values
C                   IF        Flag = *ON               /* Check if the flag is on */

8. What are op-codes? Give some examples.

Op-codes, short for operation codes, are instructions executed by a CPU or other processor. They are numeric or symbolic codes that specify a particular operation to be performed, such as adding two numbers, loading data from memory, or jumping to a different part of the program.

Examples of op-codes include:

• ADD (Add two numbers)
• SUB (Subtract two numbers)
• LOAD (Load data from memory into a register)
• STORE (Store data from a register into memory)
• JMP (Jump to a different instruction)
• CMP (Compare two values)

These vary significantly depending on the architecture, for example, x86-64 opcodes are different to ARM opcodes.

9. Explain the use of the `IF` and `ELSE` statements in RPG.

In RPG, the IF and ELSE statements control the flow of execution based on a condition. The IF statement evaluates a boolean expression. If the expression is true, the code block following the IF statement is executed. If the expression is false, the code block is skipped. An optional ELSE statement can be used after the IF block. If the IF condition is false, the code block following the ELSE statement is executed. ELSEIF can also be used for evaluating sequential conditions.

10. How do you perform calculations in RPG?

In RPG, calculations are primarily performed using the EVAL opcode or the older calculation opcodes like ADD, SUB, MULT, and DIV. EVAL is generally preferred for its flexibility and readability as it allows for complex expressions similar to those in other programming languages. For example, EVAL result = a + b * c would calculate the expression and assign the result to the variable result. Older opcodes require specifying operands and a result field separately; for example, ADD a b result would add a and b, placing the sum in result.

Beyond basic arithmetic, RPG also supports various built-in functions (BIFs) that can be used within EVAL statements for more advanced calculations. Examples include %SQRT for square root, %REM for remainder, and functions for date/time arithmetic. Conditional logic using IF statements can also be incorporated to perform calculations based on specific criteria.

11. What is a loop in programming, and how do you implement different types of loops (e.g., `FOR`, `DO`) in RPG?

In programming, a loop is a control flow statement that allows code to be executed repeatedly based on a condition. It avoids code duplication and makes it easy to process data sets or perform actions multiple times.

RPG (Report Program Generator) supports various loop constructs, primarily using DO groups. FOR loops are not directly available in the same way as in languages like C or Java. Instead, RPG uses DO groups combined with control statements like LEAVE (to exit the loop) and ITER (to skip to the next iteration) for more flexible loop control. Examples:

• Basic DO loop:

  DOW   NOT %EOF(myfile);
     READ myfile;
     // Process record
  ENDDO;
  

• Counter-controlled DO loop:

  DOW ctr <= 10;
     // Code to be executed
     ctr = ctr + 1;
  ENDDO;
  

• DO loop with LEAVE (break):

  DOW  *blanks = *blanks;
     IF condition;
        LEAVE;
     ENDIF;
     //Code here
  ENDDO;
  

• DO loop with ITER (continue):

    ```rpgle
    DOW ctr <= 10;
       IF condition;
          ITER;
       ENDIF;
       // Code to be executed if condition is false
       ctr = ctr + 1;
    ENDDO;
    ```
  

12. How do you display output to the screen in RPG?

In RPG, you primarily use the DSPLY opcode to display output to the screen. The basic syntax involves specifying the data you want to display. For instance, DSPLY MessageVar; would display the contents of the variable MessageVar on the screen. You can also display literal values directly, such as DSPLY 'Hello World';.

Besides DSPLY, output can also be displayed using output specifications within a printer file (even if it's only to be viewed on screen through WRKSPLF). You define the output fields and their positions in the DDS (Data Description Specifications) of the printer file, and then write to this printer file in your RPG program to display the formatted output.

13. What is a subfile, and why is it used?

A subfile is a display file construct used primarily in IBM i (AS/400) systems to display multiple records on a single screen. Instead of showing one record at a time, like a traditional display file, a subfile allows a user to scroll through a list of records within a defined window on the screen.

Subfiles are used because they provide an efficient way to display and interact with a set of related data. They are beneficial when dealing with data like lists of customers, orders, or items, as they allow users to view and process multiple records at once, improving usability and reducing the need to navigate between different screens. They are widely used for creating user-friendly applications on the IBM i platform.

14. Can you explain how to read data from a database file in RPG?

In RPG, reading data from a database file typically involves using the CHAIN, READ, READE, READP, and READPE opcodes. CHAIN is used for reading a specific record by key, while READ retrieves the next record sequentially. READE reads the next record that matches a specified key, and READP and READPE read the previous record sequentially and by key, respectively. Before any read operation, the file must be opened using the F-spec in the RPG program.

Here's a simplified example using CHAIN:

     FMyFile   IF   E           K DISK
     D CustID          S             10A

     C                   EVAL      CustID = '12345'
     C     CustID        CHAIN     MyFile                  99
     C     99              IFEQ      *OFF
     C                   DSPLY                   'Record Found'        
     C                   ENDIF

In this example, MyFile is opened as an externally described file. The CHAIN opcode attempts to read a record from MyFile where the key field matches the value in CustID. Error handling (indicator 99) checks if the record was found.

15. How do you update records in a database file using RPG?

To update records in a database file using RPG, you typically use the UPDATE operation code within a logical unit of work. First, read the record to be updated using a chain (CHAIN) or read (READ, READE, READP, READPE) operation. After reading the record, modify the relevant fields in the RPG program's record format. Finally, use the UPDATE opcode along with the record format name and the file name to write the changes back to the database file. The file must be opened for update (*UPDATE mode) to allow this operation.

For example:

C CHAIN KEY_FIELD FILE1 REC1
C IF %FOUND(FILE1);
C EVAL FieldToUpdate = NewValue;
C UPDATE REC1 FILE1;
C ENDIF;

In this example, if a record with KEY_FIELD is found in FILE1, the FieldToUpdate is updated and the changes are written back using UPDATE REC1 FILE1.

16. What are the different file types you can use in an RPG program?

RPG programs can interact with several file types. The most common include:

• Source physical files: Used to store the RPG source code itself. These usually have a naming convention like QRPGLESRC. Example: CRTPF FILE(MYLIB/QRPGLESRC) RCDLEN(112). Source code is typically entered via SEU or RDi.
• Physical files: Standard database files containing data records. These are fundamental for data storage and retrieval. DDS (Data Description Specifications) defines the record formats.
• Logical files: These are view-only files based on one or more physical files. They do not contain actual data, but provide alternative access paths (indexes) or subsets of data from physical files. CRTLF creates the logical file.
• Printer files: Used for generating reports and other printed output. These are defined using DDS and control the formatting of printed data. CRTPRTF creates a printer file.
• Display files: Used to define interactive screens for user interaction. These are also defined with DDS and specify the layout of input and output fields on the screen. CRTDSPF creates a display file.
• Externally described data structures: Data structures defined outside the RPG program (e.g., in a database table or file). RPG programs can then use these external data structures to access and manipulate the data.

17. What is the purpose of the File Description Specifications (F-specs)?

File Description Specifications (F-specs) define the structure and characteristics of data files. They serve as a blueprint, specifying details like the record length, field definitions (name, data type, and length), and the order in which fields appear within each record. This ensures that data is consistently interpreted, regardless of the system or application accessing it.

Essentially, F-specs enable programs to correctly read, write, and process data stored in external files. Without them, programs would struggle to understand the format of the data, leading to errors or data corruption. They are critical for data interoperability and reliable data processing.

18. What is the purpose of the Input Specifications (I-specs)?

Input Specifications (I-specs) define the expected format, type, range, and validation rules for data that a system or component receives as input. They serve as a contract between data providers and consumers, ensuring data quality and consistency.

They outline what is considered valid input, allowing systems to handle data predictably, prevent errors, and ensure reliable operation. I-specs also guide developers during implementation and testing by providing clear expectations regarding input data.

19. What is the purpose of the Calculation Specifications (C-specs)?

C-specs, or Calculation Specifications, in RPG (Report Program Generator) define the logic and operations performed within a program. They are used to specify calculations, data manipulation, and decision-making processes.

Essentially, C-specs dictate what the program does with the data it receives. They define the flow of operations, including arithmetic calculations, string manipulations, data movement, and calls to subroutines or other programs. These specifications work in conjunction with other specification types (like input and output specs) to create a complete RPG program. They can include operations like:

• ADD, SUB, MULT, DIV (Arithmetic operations)
• MOVE, MOVEL (Data movement)
• COMP (Compare)
• IF, ELSE, ENDIF (Conditional logic)
• CALL, CALLB (Subroutine calls)
• DOW, DOU, FOR, ENDDO, ENDFOR (Looping)

20. What is the purpose of the Output Specifications (O-specs)?

The purpose of Output Specifications (O-specs) is to clearly and precisely define the expected outputs of a system, module, or program. They serve as a blueprint for developers, testers, and other stakeholders, ensuring everyone understands what the system should produce under various conditions. O-specs are crucial for verification and validation activities.

Specifically, O-specs typically detail the format, content, structure, and units of measurement for each output. This can include things like file formats (e.g., CSV, JSON), data types, error messages, user interface elements, or reports. By having a well-defined O-spec, developers can write code to generate the specified output, and testers can verify that the actual output matches the expected output.

21. What is a program status data structure (PSDS), and what information does it provide?

A Program Status Data Structure (PSDS) is a data structure that holds information about the current state of a running program. It provides a snapshot of the program's execution at a given point in time, useful for debugging, monitoring, and understanding program behavior.

Information in a PSDS typically includes:

• Program Counter (PC): The address of the next instruction to be executed.
• Registers: The values stored in the CPU's registers.
• Stack Pointer (SP): The current position of the stack.
• Memory Management Information: Details about memory allocation and usage.
• Status Flags: Indicators of various conditions (e.g., zero flag, carry flag).
• I/O Status: Information about input/output operations.
• Error codes: If any errors occurred during program execution.

22. How do you handle errors in an RPG program?

RPG provides several mechanisms for error handling. ILE RPG (RPG IV) leverages exception handling using MONITOR, ON-ERROR, and ENDMON blocks. Within a MONITOR block, code that might generate an error is executed. The ON-ERROR block then catches specific error codes (e.g., status codes from file operations) or general exceptions, allowing the program to take corrective action, log the error, or terminate gracefully. The *PSSR subroutine (Program Status Subroutine) can be used as a global error handler.

Traditional RPG also relies on status codes and indicator variables. After each operation (e.g., file I/O, calculations), the program checks the status code in the *STATUS variable or specific indicators (e.g., *IN01 - *IN99, *INLR, *INRT). If the status code or an indicator suggests an error, the program can branch to an error handling routine or display an error message. Older RPG versions might utilize the GOTO statement to jump to specific error routines.

23. What are indicators in RPG, and how are they used?

In RPG (Report Program Generator), indicators are single-character variables that hold either a *ON or *OFF value, representing a true or false condition. They act as switches to control program flow, record selection, field editing, and output. Indicators are used to conditionally execute code or perform specific actions based on the state of the program or data being processed.

Indicators are used in various ways, for example:

• Conditional Compilation: Control which code is included during compilation.
• Record Selection: Determine which records from a file are processed based on certain criteria.
• Conditional Execution: Control if a calculation, output, or other operation happens. For example:

  C     IF        *IN50 = *ON
  C                   DSPLY    'Indicator 50 is ON'
  C     ENDIF
  

• Field Editing: Modify the appearance of output fields.
• Error Handling: Signal the occurrence of an error condition.

24. Explain the concept of modular programming in RPG.

Modular programming in RPG involves breaking down a large program into smaller, independent, and reusable modules (procedures or subroutines). This approach enhances code organization, readability, and maintainability. Instead of a monolithic program, you have a collection of specialized modules, each performing a specific task.

Benefits include:

• Improved code reusability: Modules can be called from multiple parts of the program, reducing code duplication.
• Simplified debugging: Easier to isolate and fix errors within a specific module.
• Increased code maintainability: Changes to one module have minimal impact on other modules.
• Enhanced code readability: Modules with well-defined purposes make the program easier to understand. Example: callp CalculateTax(OrderTotal : TaxAmount);

25. What is the difference between a program and a module in RPG?

In RPG (specifically RPG IV or ILE RPG), the key difference lies in how code is structured and executed.

A program is a standalone, executable unit. When you call a program, the entire program is loaded and executed. It generally follows a monolithic structure, although it can call subroutines or other programs. A module, on the other hand, is a smaller, reusable unit of code that cannot be run independently. Modules are designed to be compiled separately and then bound together to create a program or service program. This modular approach promotes code reuse and maintainability. Modules are used to group related procedures or functions and can be part of one or more programs or service programs.

Key differences:

• Execution: Programs are directly executable; modules are not.
• Structure: Programs can be monolithic or modular (via subroutines); modules must be modular and reusable.
• Compilation: Modules are compiled independently; programs are often built by binding multiple modules together. This allows for a more organized and efficient development process.
• Reusability: Modules promote code reuse, while Programs may or may not be reusable.

26. How do you call a sub-procedure from within an RPG program?

In RPG, you call a subprocedure using a CALLB operation code or by simply using the subprocedure name as if it were a built-in function. The CALLB opcode is typically used when you need to handle return values and potential exceptions explicitly. Alternatively, you can directly call the subprocedure by its name, passing any required parameters within parentheses. This is the preferred and most common method.

For example:

// Using CALLB
CALLB mySubProc;  // if no parameters
CALLB mySubProc(parm1 : parm2); // with parameters

// Direct call (preferred)
mySubProc(); //if no parameters
mySubProc(parm1 : parm2); // with parameters

27. What are some of the debugging tools available for RPG programs?

RPG programs offer various debugging tools. The most common is the STRDBG command, which starts the interactive debugger. Within the debugger, you can set breakpoints, display and modify variable values, and step through the code line by line. CL commands like DSPPGMVAR (Display Program Variable) and CHGVAR (Change Variable) can also be used in conjunction with STRDBG or independently for quick checks.

Another option is the Service Entry Point (SEP) debugging feature, which allows you to debug production programs with minimal performance impact. SEPs enable you to monitor variables and program flow without stopping the program entirely. Additionally, tools like IBM Rational Developer for i (RDi) provide a graphical interface for debugging, offering features like visual breakpoints, data monitoring, and call stack analysis. The output from commands like DSPLOG can also be helpful for examining program behavior and errors after execution.

28. What is SQLRPGLE in IBM i, and what are its benefits?

SQLRPGLE is RPGLE (RPG IV) code embedded with SQL statements. It allows you to directly embed SQL statements within your RPG programs to interact with databases. Instead of using traditional record-level access methods, SQLRPGLE uses SQL for data manipulation.

Benefits include:

• Improved Performance: SQL can optimize data access and retrieval, potentially leading to faster execution than traditional record-level I/O. Uses the power of the database engine, typically much more performant than native record level access.
• Simplified Data Access: SQL provides a declarative way to define the data you need, rather than specifying how to navigate the database. SELECT * FROM MYTABLE WHERE COLUMN1 = 'VALUE' is more concise than the equivalent native RPG.
• Data Integrity: Using SQL enforces database constraints and referential integrity, helping to ensure data quality.
• Portability: SQL is a standard language, making it easier to migrate applications to other database platforms (with appropriate adjustments). SQL is SQL regardless of the underlying RPG layer.
• Modernization: SQLRPGLE allows RPG programs to take advantage of modern database features and technologies.

IBM RPG interview questions for juniors

1. What is RPG in simple terms? Can you relate it to anything else a five-year-old might know?

RPG stands for Role-Playing Game. Imagine you're playing pretend! In an RPG, you choose a character like a knight, a wizard, or even a brave puppy, and you act out their adventures. You make decisions for them, like what to say or where to go, and those choices change the story.

Think of it like playing with LEGOs and making up a story as you go. You decide what your LEGO people do, where they go, and what happens to them. An RPG is just like that, but usually with rules or dice rolls to help decide what happens, especially when it comes to fighting monsters or solving puzzles. Some RPGs are video games, like pretending you're Mario saving Princess Peach, but others are played around a table with friends!

2. Imagine you have a toy box. How would you tell the computer to find a specific toy using RPG?

Using RPG, I would define the toy box as a data structure, perhaps an array where each element represents a slot in the toy box and the value is the toy in that slot (or *BLANK if empty). To find a specific toy, I would iterate through the array using a FOR loop or DOW loop. Inside the loop, I'd use an IF statement to check if the current element's value (the toy) matches the target toy I'm looking for. If a match is found, I'd set a flag (like ToyFound = *ON) and possibly record the array index where the toy was located. If the loop completes without finding the toy, the flag would remain *OFF, indicating the toy wasn't in the box.

For example, conceptually in RPG:

DCL-S ToyBox QUALIFIED DIM(10);
  Toy VARCHAR(20);
END-DS;

DCL-S TargetToy VARCHAR(20) INZ('Teddy Bear');
DCL-S ToyFound IND INZ(*OFF);
DCL-S i INT(10);

FOR i = 1 TO %ELEM(ToyBox);
  IF ToyBox(i).Toy = TargetToy;
    ToyFound = *ON;
    // Do something with the found toy
    LEAVE;
  ENDIF;
ENDFOR;

IF ToyFound;
  DSPLY 'Toy Found!';
ELSE;
  DSPLY 'Toy Not Found.';
ENDIF;

3. What does 'compiling' mean in RPG, like when you're building with LEGOs?

Compiling in RPG (Report Program Generator) is like taking all your individual LEGO bricks (your RPG code) and following a set of instructions (the RPG compiler) to assemble them into a complete LEGO model (an executable program). The compiler checks that the instructions (RPG code) are valid and then translates them into a language the computer understands (machine code).

Specifically, the RPG compiler takes your human-readable RPG source code and transforms it into an object program. This object program is then linked with other object programs and system libraries to create an executable program that the IBM i operating system can run. Without compiling, your RPG code is just text; the compiler makes it functional.

4. If data is like toys, what are variables in RPG? How do you name these 'toy containers'?

If data (toys) exists in an RPG, variables are like containers (toy boxes) that hold those toys. They allow the RPG to store, access, and modify the game's data. For example, a player's health points, the number of potions they have, or the current level of a skill are all stored in variables.

Naming these 'toy containers' (variables) should be descriptive and meaningful. Here are some conventions:

• Use camelCase: playerHealth, numberOfPotions
• Be specific: swordDamage instead of just damage
• Avoid abbreviations unless they're very common: HP for health points is acceptable.
• Use prefixes/suffixes for different data types if needed, but generally rely on strong typing to ensure data integrity. For example, in RPGLE/CL:

  dcl-s playerHealth int(10);  // Integer variable for player's health
  dcl-s playerName varchar(50); // Character variable for player's name
  

5. Explain 'fixed-form' versus 'free-form' RPG like you're describing different ways to draw.

Imagine drawing with stencils (fixed-form) versus drawing freehand (free-form). In a fixed-form RPG like, say an older COBOL RPG, you're constrained to specific areas on the screen or output. Each column and row has a designated purpose; you're essentially filling in pre-defined templates. Data has to fit exactly within these pre-set boundaries.

In contrast, a free-form RPG, such as RPGLE, is like drawing without stencils. You have much more flexibility in defining your data structures, and how your program flows. Instead of being bound by column positions, you declare variables and use structured programming constructs like IF/ELSE and DO/ENDDO without those rigid positional restraints. Think of it as moving from painting by numbers to creating your own masterpiece.

6. What is a 'subroutine' in RPG? Imagine you're teaching a robot a short dance routine.

In RPG (Report Program Generator), a subroutine is like a mini-program or a reusable block of code within a larger RPG program. Think of it as teaching our robot a specific dance move, like a 'spin' or a 'jump'. Instead of writing the code for the spin every time you want the robot to spin, you define it once as a subroutine and then call it whenever needed. This avoids repetition and makes the main program easier to read and manage.

A subroutine starts with a BEGSR (Begin Subroutine) statement and ends with an ENDSR (End Subroutine) statement. You call the subroutine using the EXSR (Execute Subroutine) operation code followed by the subroutine's name. Subroutines can accept parameters and return values, which allows for even greater flexibility and code reusability. Here's a simple example:

     /FREE
      // Main Program
      dsply 'Main Program Start';
      exsr MySubroutine; // Call the subroutine
      dsply 'Main Program End';
      *INLR = *ON;
      
      // Subroutine Definition
      begsr MySubroutine;
        dsply 'Inside MySubroutine';
      endsr;
     /END-FREE

7. What are 'indicators' in RPG? How do they help you decide what to do next in your program, like traffic lights?

In RPG, indicators are single-character flags (usually *INxx, where xx is a number from 01 to 99, or *INLR for Last Record indicator, etc.) that hold a binary value: either 'on' (1) or 'off' (0). They act like traffic lights, signaling the status of a condition or the result of an operation.

Indicators guide program flow by determining which sections of code should be executed. For example, an indicator might be turned on if a record matches a certain criteria or if a calculation results in an error. Subsequent RPG statements can then be conditionally executed based on whether the indicator is on or off, like this example:

C     IF        *IN01
C     DISP      'Indicator 01 is on'
C     ENDIF

8. How would you use RPG to add two numbers together? Pretend they're the number of candies you and your friend have.

In RPG, you'd use the ADD opcode to add two numeric fields together. Assuming we have two fields defined, one for my candies and one for my friend's candies, the RPG code would look something like this:

DCL-S MyCandies PACKED(5:0) INZ(10); // I have 10 candies
DCL-S FriendCandies PACKED(5:0) INZ(5); // My friend has 5 candies
DCL-S TotalCandies PACKED(5:0) INZ(0);

ADD MyCandies FriendCandies TotalCandies;

DSPLY TotalCandies; // Display the total (15)

This code declares three numeric variables: MyCandies, FriendCandies, and TotalCandies. It initializes MyCandies to 10 and FriendCandies to 5. The ADD opcode adds the values of MyCandies and FriendCandies and stores the result in TotalCandies. Finally, the DSPLY opcode displays the value of TotalCandies (which will be 15).

9. What is a 'file' in RPG? Is it like a notebook or a computer file?

In RPG, a 'file' is conceptually similar to both a notebook and a computer file, but with specific characteristics. It represents a structured collection of data, analogous to a physical file cabinet or notebook containing records. However, unlike a physical notebook, an RPG file is defined programmatically, specifying the data's structure and how it's accessed. It defines the record format, including field names, data types, and lengths.

Think of it this way: in RPG, you describe the 'file' structure in your program (similar to defining a class or structure in other languages). The RPG program then uses this definition to interact with the actual data, which might reside in a database table (a physical file in IBM i terminology) or another data source. The 'file' in the RPG program therefore acts as a bridge (or interface) between the program logic and the underlying data storage. The actual underlying data structure is a physical file, if you would like to create one, you would do so using the CRTPF CL command. The file declaration is called a logical file.

10. What is the difference between 'character', 'numeric', and 'date' data types in RPG?

In RPG, character, numeric, and date are fundamental data types:

• Character: Stores alphanumeric data (letters, numbers, and special characters). It's used for text-based information like names, addresses, or descriptions. Character fields have a fixed length.
• Numeric: Stores numerical data, used for calculations. RPG supports various numeric formats like integer, packed decimal, and floating-point, each offering different precision and storage efficiency.
• Date: Stores calendar dates. RPG provides built-in functions to perform date arithmetic and formatting. Dates are typically stored in a specific format (e.g., ISO, MDY, DMY) as defined by the programmer or system defaults.

11. Explain what a 'loop' is in RPG, like going around in a circle until you're dizzy.

Imagine a character in a role-playing game (RPG) stuck walking in a circle. That's similar to a 'loop' in programming. A loop is a sequence of instructions that the computer repeats over and over again until a specific condition is met. For example, in RPG code, a loop might continuously check if the player's health is below zero. If it is, the loop ends, and the game character is declared dead. If not, the loop continues, and the game character remains alive.

Here's a simplified example in pseudocode:

while (playerHealth > 0) {
    // Player takes damage
    playerHealth = playerHealth - 10;
    // Check if health is zero or less
    if(playerHealth <= 0) {
         //Player is dead
         print("Game Over");
    }
}

In this example the code inside the while loop repeats until playerHealth is not greater than 0.

12. What does 'debugging' mean? How do you find mistakes in your program, like finding a broken toy?

Debugging is like being a detective for your code! It means finding and fixing problems (bugs) that make your program not work as expected. Think of it like finding out why a toy isn't working.

To find mistakes, I use a few tricks. First, I carefully read the code to see if I made any obvious typos or logic errors. I also use print statements (like console.log() in JavaScript or print() in Python) to display the values of variables and understand what's happening at different points in the program. Another useful technique is using a debugger. A debugger allows you to step through your code line by line, inspect variables, and pause execution to see what's going on. This can help pinpoint exactly where the problem occurs.

13. Can you name a few built-in functions RPG provides? What simple tasks do they help with?

RPG provides several built-in functions (BIFs) to simplify common tasks. A few examples include:

• %SUBST(string:start:length): Extracts a substring from a given string. For example, if you have a field 'Name' containing 'John Doe', %SUBST(Name:1:4) would return 'John'.
• %TRIM(string): Removes leading and trailing blanks from a string. This is helpful when dealing with user input or data from external sources where spacing might be inconsistent.
• %INT(numeric): Converts a value to an integer. This is useful for data type conversions when you need to perform calculations on numeric values represented as strings or packed decimals.
• %CHAR(numeric): Converts a numeric value to a character string.
• %DATE(string:format): Converts a character string to a date value, based on the specified format. format specifies how the date is represented in string.

14. Explain what an 'array' is. Imagine it's a shelf where you store many similar toys.

An array is a fundamental data structure in programming. Think of it like a shelf holding similar items (toys, in your analogy). It's a collection of elements of the same data type (e.g., all numbers, all strings) stored in contiguous memory locations. Each element can be accessed using its index, which is its position in the array, starting from 0. For example, on the shelf, the first toy is at position 0, the second at position 1, and so on.

Arrays are useful because they allow you to efficiently store and access large amounts of related data. Many programming languages have built-in support for arrays. Here's an example in Python:

my_array = [10, 20, 30, 40, 50]
print(my_array[0])  # Access the first element (value 10)

15. What is the purpose of a 'cycle' in RPG? How does RPG know when to stop?

In RPG (Report Program Generator), a 'cycle' refers to the iterative process of reading a record, processing it, and then writing the output. The purpose of the cycle is to automate the handling of data records from an input file, performing calculations or manipulations based on the record's contents, and generating output reports or updated files. This simplified the process before databases were common, and programs commonly read entire files sequentially.

16. What is a 'record format'? How does it describe the structure of data in a file?

A 'record format' defines the structure of data within a file. It specifies the types, sizes, and order of fields that make up each record in the file. Think of it as a blueprint or template that dictates how data is organized and stored.

Specifically, the record format describes the following aspects of data:

• Field names: Each piece of data within a record has a name.
• Data types: The type of data each field will hold (e.g., integer, string, date).
• Field length: The size or number of characters allocated for each field.
• Field order: The sequence in which the fields appear within the record.
• Delimiters (optional): Characters used to separate fields or records (e.g., commas, tabs, newline characters).

17. Describe the difference between 'read' and 'write' operations in RPG.

In RPG, READ and WRITE operations are fundamental for data access. READ operations are used to retrieve data from a file (or device). For example, READ MYFILE; attempts to read the next record from the file MYFILE into the program. Conversely, WRITE operations are used to add new records to a file. WRITE MYFILE record_data; adds record_data as a new record to MYFILE.

The key difference lies in their purpose: READ is for input (retrieving existing data), while WRITE is for output (creating new data). They interact with files differently; READ expects the file to exist and have records to retrieve, whereas WRITE creates a new record at the end of the specified file (or creates the file if necessary).

18. What is the significance of the 'Control' specification (H-spec) in RPG?

The Control specification (H-spec) in RPG is crucial as it defines the global characteristics of the RPG program or module. It acts as the configuration file, setting up the environment in which the code will run.

Specifically, it controls aspects such as the RPG version used, the type of program being created (e.g., program, service program), date format, decimal format, compilation options, and the default handling of errors. Without a correctly configured H-spec, the program may not compile or might behave unexpectedly due to incorrect settings. You can specify compiler directives here to impact performance.

19. What are 'named constants'? Why are they useful in an RPG program?

Named constants are symbolic names given to literal values that do not change during the execution of a program. Instead of using the literal value directly, you use the name. For example, instead of using 3.14159 for Pi, you might define a constant PI = 3.14159. In languages like C++, this might be declared using const double PI = 3.14159; or #define PI 3.14159.

In an RPG program, named constants improve readability and maintainability. For instance, instead of repeatedly using the literal 100 to represent the maximum health points of a character, you could define a constant MAX_HEALTH = 100. This makes the code easier to understand. If you later need to change the maximum health, you only need to modify the constant's definition, rather than searching for every instance of 100 in your code, which reduces the risk of errors and makes updates simpler.

20. What is the purpose of the 'Move' operation (MOVE) in RPG?

The MOVE operation in RPG is used to copy data from one field (the source) to another field (the target). It's primarily used for data transfer and conversion. MOVE handles data type conversions automatically, attempting to convert the source data type to the target data type if they are different. If a direct conversion isn't possible, RPG may truncate the source data to fit the target field, or generate an error. For example, one could MOVE a numeric value to a character field to represent it as text.

While MOVE is a legacy operation, its purpose is often fulfilled by more modern and flexible operations like %CHAR, %DEC, and direct assignment (=) in modern RPG code (RPGLE). The direct assignment along with data type conversion functions are generally preferred for better code readability and maintainability. However, understanding MOVE is essential when working with older RPG codebases.

21. Can you explain what a 'parameter' is in RPG? Why are parameters useful?

In RPG, a parameter is a value that is passed to a subprocedure or program. Think of it as an input that the subprocedure or program needs to do its job. Parameters allow you to provide specific data to the called routine without relying on global variables.

Parameters are useful because they promote modularity, reusability, and code clarity. By passing parameters, you can make your subprocedures and programs more general-purpose, allowing them to be used in different contexts with different data. This reduces code duplication and makes your code easier to understand and maintain. DCL-PROC MySubProc; DCL-PI MySubProc; Parm1 CHAR(10) CONST; Parm2 INT(10) VALUE; END-PI; // ... code using Parm1 and Parm2 ... END-PROC; shows the declaration of parameters in a RPG subprocedure.

22. What is the 'Display File' in RPG? How is it used to show information to the user?

In RPG, a 'Display File' is an external object that defines the layout and characteristics of a screen presented to the user. It acts as an interface between the RPG program and the user's terminal.

It's used to show information by defining fields (data areas) on the screen. The RPG program writes data to these fields in the display file. When the RPG program executes an output operation (e.g., EXFMT), the contents of these fields are displayed on the user's screen. The display file also specifies input fields, allowing the user to enter data that the RPG program can then read using an input operation.

23. What is the 'Update' operation (UPDATE) used for in RPG?

The UPDATE operation in RPG is used to modify existing records in a database file. It changes the values of one or more fields in a record that has been previously read using a chain, read, or other input operation. The update operation typically follows a read operation that positions the file at the record to be updated. You specify which fields to update by assigning new values to the corresponding field names after the UPDATE keyword.

For example, if a customer's address needs to be changed, an RPG program would first CHAIN to read the customer record based on the customer number. Then, it would assign the new address values to the appropriate fields (e.g., Address, City, State, Zip) and finally use the UPDATE operation to write the modified record back to the database.

24. How can you handle errors in RPG? What happens if something goes wrong during the program?

RPG provides several mechanisms for handling errors. You can use the *INZSR (Initialization Subroutine) to set up error handling at the start of the program. The MONITOR group allows you to trap exceptions within a block of code. If an error occurs within the MONITOR block, control passes to the corresponding ON-ERROR or ON-EXCP block for specific error codes or exception types. You can also use the *PSSR (Program Status Subroutine) to handle unmonitored errors or errors that occur outside of a MONITOR group.

When an error occurs in RPG without proper error handling, the program might terminate abnormally, which can lead to data corruption or inconsistent results. The specific behavior depends on the severity of the error and the system's error handling configuration. By implementing error handling routines such as using MONITOR, ON-ERROR, and *PSSR, you can gracefully handle exceptions, log errors, and take corrective actions to prevent program termination, or at least control it.

25. What is the difference between a 'compile-time' and 'run-time' error?

Compile-time errors are detected by the compiler before the program starts running. These errors typically relate to syntax, type mismatches, or violations of the language's rules. Examples include:

• Syntax errors (e.g., missing semicolon)
• Type errors (e.g., assigning a string to an integer variable)
• Undeclared variables

Run-time errors, on the other hand, occur while the program is executing. The compiler doesn't catch these because they depend on the program's input or execution environment. These errors often lead to program crashes or unexpected behavior. Common examples are:

• Division by zero
• Null pointer exceptions
• Array index out of bounds
• Memory allocation errors

26. Describe the purpose of the 'Select' group in RPG. How does it make decisions?

The Select group in RPG is used to execute one block of code from a set of mutually exclusive choices. It functions as a structured IF-ELSEIF-ELSE construct. The Select group begins with a SELECT operation and ends with an ENDSL operation. Within the group, each possible choice is defined by a WHEN operation, containing a conditional expression. The first WHEN condition that evaluates to true will have its associated code block executed. Optionally, a OTHER operation can be included to define a block of code to execute if none of the WHEN conditions are met, similar to an ELSE clause.

The decision-making process within a Select group relies on evaluating the logical expressions specified in each WHEN statement. RPG evaluates these expressions sequentially, from top to bottom. As soon as one WHEN expression results in a 'true' value, the program executes the corresponding block of code and then immediately jumps to the ENDSL statement, bypassing any remaining WHEN or OTHER blocks. If no WHEN condition is true, the OTHER block (if present) will be executed. If no OTHER block is present and no WHEN conditions are true, control passes directly to the statement following the ENDSL.

27. What is the role of the 'Input' specification (I-spec) in RPG?

In RPG (Report Program Generator), the Input specification (I-spec) defines the characteristics of the input data used by the program. It describes the structure of the input records, the fields within those records, and how the data should be read and processed. The I-spec essentially tells the RPG compiler what the input data looks like. It also associates field names with the physical locations in the input record.

Specifically, the I-spec:

• Defines record identification codes for record types.
• Specifies field locations (starting and ending positions within the record). e.g. 1 5 CustomerID means that the CustomerID is located in the beginning at position 1 and ends at position 5 of the current record.
• Allows for field validation using indicators.
• Associates fields with record types.
• Can be used to define arrays from input data.

28. What is a 'Commitment Control'? How does it ensure data integrity?

Commitment control, also known as transaction management, is a mechanism used in database systems to ensure data integrity and consistency, especially during concurrent access and system failures. It treats a sequence of database operations as a single logical unit of work, called a transaction.

Commitment control ensures data integrity by enforcing the ACID properties: Atomicity (all or nothing), Consistency (maintains database invariants), Isolation (concurrent transactions appear to execute in isolation), and Durability (committed changes are permanent). It uses techniques like logging, locking, and two-phase commit to achieve these properties. For example, if a transaction fails midway, the system can roll back all changes made by that transaction, restoring the database to its previous consistent state. This prevents partial updates and ensures that data remains reliable.

IBM RPG intermediate interview questions

1. Explain the difference between a subprocedure and a subroutine in RPGLE.

In RPGLE, the terms subprocedure and subroutine are often used interchangeably, but there's a subtle distinction. A subroutine is a block of code within a program, defined using the BEGSR (Begin Subroutine) and ENDSR (End Subroutine) opcodes. It's called using the EXSR (Execute Subroutine) opcode. Subroutines have a global scope; they can access all variables defined in the main program. They are older coding style.

A subprocedure, on the other hand, is a more structured and modern approach introduced with ILE (Integrated Language Environment). It's defined using the PROC (Procedure) and ENDP (End Procedure) keywords. Subprocedures offer local scoping; they can have their own parameters, return values, and local variables, thus promoting modularity and code reusability. They are invoked like a function call and allow for better encapsulation.

2. How do you handle exceptions (errors) in RPGLE programs?

In RPGLE, exceptions (errors) are primarily handled using the MONITOR, ON-ERROR, and ENDMON op-codes. The MONITOR block surrounds the code that might produce an exception. If an error occurs within this block, control is transferred to the ON-ERROR block. The ON-ERROR block specifies the error codes to handle. Multiple ON-ERROR blocks can exist to handle different error conditions.

For example:

     MONITOR;
       // Code that might cause an exception
       CALL programThatMightFail;

     ON-ERROR *PROGRAMSTATUS 426; // File open error
       // Handle the file open error
       dsply 'File open error!';

     ON-ERROR *ALL;
       // Handle any other error
       dsply 'Some other error occurred!';

     ENDMON;

Another mechanism involves checking the program status data structure (PSDS) after potentially problematic operations. The PSDS contains error codes and other relevant information. However, MONITOR groups are generally preferred for structured exception handling.

3. What is the purpose of the COMMIT and ROLLBACK operations in RPGLE, and how do you use them?

The COMMIT and ROLLBACK operations in RPGLE are used for transaction management, ensuring data integrity in database updates. COMMIT permanently saves all changes made to the database since the last commit point. Conversely, ROLLBACK discards all changes made since the last commit point, reverting the database to its previous state. They are usually used in conjunction.

Here's how you would typically use them:

1. Start a transaction (implicitly when the first update occurs after program starts or a previous commit/rollback).
2. Perform multiple database update operations (e.g., UPDATE, DELETE, INSERT).
3. If all operations are successful and should be saved, execute the COMMIT operation. If any operation fails or the transaction needs to be abandoned, execute the ROLLBACK operation. COMMIT is coded as COMMIT; and ROLLBACK is coded as ROLLBACK; within RPGLE source code. These are normally used in conjunction with the *ISO commit control keyword on the H-Spec.

4. Describe how you would use a user space in RPGLE.

User spaces in RPGLE provide a mechanism for storing and retrieving data that can be shared between different programs or even different activations of the same program. I would use a user space to persist data that needs to be accessed by multiple RPGLE programs, such as configuration settings, shared counters, or intermediate results from a batch process.

To use a user space, I would first create it using the CRTSPF command. In RPGLE, I'd then use the User Space APIs, such as QUSCRTUS (Create User Space), QUSRUS (Retrieve User Space Information), QUSCHGUS (Change User Space), and QUSDLTUS (Delete User Space) to manage the user space. I'd then use data structures mapped to the user space to read and update the data. For example, to retrieve data I would use QUSRTVUS (Retrieve User Space) with pointers to the user space, and to update the user space I would use QUSCHGUS or QUSPTRUS (Change User Space) in conjunction with pointers. Proper locking mechanisms may be needed to ensure data integrity when multiple programs access the same user space concurrently.

5. What are the advantages of using embedded SQL in RPGLE?

Embedded SQL in RPGLE offers several advantages. First, it allows direct access to database data within the RPGLE program, simplifying data manipulation. Instead of relying on external procedures or APIs, SQL statements are integrated directly into the RPGLE source code, providing a more seamless and potentially performant way to interact with the database.

Second, embedded SQL often leads to better code maintainability. SQL statements are generally easier to understand and modify compared to complex native file I/O operations or using externally called stored procedures. Using SQL's declarative nature, you only specify what data you want, not how to retrieve it. This allows you to more easily change how data is retrieved or what data is retrieved when compared to other data access methods available in RPGLE. Finally, using SQL can potentially lead to code portability across different database platforms if you are careful in your design.

6. Explain the concept of a service program in RPGLE.

A service program in RPGLE is a collection of procedures and data that can be called by other programs or service programs. It's essentially a reusable module that promotes modularity and code reuse. Think of it as a library of functions.

Service programs are created using the CRTSRVPGM command. They are bound to programs or other service programs using the BNDSRVPGM keyword on the CRTBNDRPG or CRTSRVPGM command. A key advantage of service programs is that changes to the service program don't necessarily require recompilation of the programs that use it, as long as the interface (procedure signatures) remains the same. This significantly reduces maintenance effort.

7. How would you implement a recursive subprocedure in RPGLE?

In RPGLE, a recursive subprocedure is implemented by defining a procedure that calls itself. Key to enabling recursion is using the NEW keyword in the procedure's definition. This ensures a new activation group is created with each recursive call, preventing variable conflicts between different levels of recursion. Without NEW, the procedure would overwrite its own data on each call, leading to unpredictable behavior.

Here's a simple example:

     dcl-proc factorial; 
       dcl-pi *n 10u 0;  
         num *n 10u 0 value; 
       end-pi; 
       dcl-s result *n 10u 0; 
 
       if (num <= 1); 
         return 1; 
       else; 
         result = num * factorial(num - 1); 
         return result; 
       endif; 
     end-proc; 

This example calculates the factorial of a number recursively. Note that there must be a condition to stop recursion (in this example the 'if' statement); otherwise the call would cause infinite loops.

8. What is the difference between a keyed file and a non-keyed file in RPGLE?

A keyed file in RPGLE utilizes an index (key) to access records directly and efficiently. Records are stored in a logical order based on the key field(s). This allows for rapid retrieval of specific records based on the key value. Operations like READ, READE, READEQ, READGT, and READGE are used with keyed files to access records by key.

In contrast, a non-keyed file (also known as arrival sequence file) has no index. Records are stored in the order they were added to the file. To find a specific record, you typically need to read through the file sequentially using the READ operation. This makes accessing specific records slower than with keyed files. Non-keyed files are often used for simple sequential processing or when the order of records is important.

9. How can you pass parameters by reference versus by value in RPGLE?

In RPGLE, you can pass parameters by reference using the *VAR keyword in the procedure interface or prototype definition. When *VAR is specified, the called procedure receives a pointer to the original variable in the calling program. Any changes made to the parameter within the called procedure directly affect the original variable. Without *VAR, parameters are passed by value, meaning the called procedure receives a copy of the variable's value, and changes do not affect the original.

For example, in the procedure interface:

Dcl-Proc MyProcedure; 
Dcl-Pi MyProcedure; 
  Parm1 Char(10) *VAR; 
end-Pi; 

Parm1 will be passed by reference. Conversely, Parm2 Char(10) would be passed by value (if *VAR is not specified).

10. Describe how you would use data structures to define complex data layouts in RPGLE.

In RPGLE, data structures are crucial for defining complex data layouts. I'd use named data structures to group related fields together under a single name, improving code readability and maintainability. For example, a customer record might have a data structure containing name, address, and contact information. Subfields within the data structure define the individual data elements and their attributes (data type, length). Additionally, qualified data structures allow referencing subfields using the data structure name, avoiding naming conflicts, especially with multiple data structures.

Arrays of data structures are particularly useful for representing repeating groups of data, such as a list of order items within an order record. Overlaying data structures allows me to redefine the same memory space with different layouts, which is useful for handling variable-length data or reinterpreting data received from external sources. Finally, utilizing externally described data structures allows importing data layouts defined in DDS or other external definitions, promoting consistency and reducing redundancy. Using these techniques, I can handle even very intricate data layouts cleanly and efficiently in RPGLE.

11. What is the purpose of the OVERLAY keyword in RPGLE, and how is it used?

The OVERLAY keyword in RPGLE is used to define a subfield within a data structure that shares the same memory space as another field (either a field in the data structure itself or an independent field). Effectively, it allows you to redefine parts of a field using a different name and/or data type. This is useful for accessing specific portions of a field or for reinterpreting the data in a different format without moving it.

OVERLAY is specified in the Data Structure definition. For example: Dcl-Ds MyDS; Dcl-Char Field1 10; Dcl-Char SubField OVERLAY(Field1 : 1 : 5); End-Ds; In this example, SubField occupies the first 5 positions of Field1. If OVERLAY is used without a length specified, the length is assumed to be the length of the field being overlaid, starting at the specified position. The general syntax is OVERLAY(base_field : start_position : length) where the length is optional and defaults to the length of the overlaying field. The starting position, if omitted, defaults to 1. Note: the EXTNAME and LIKEDS keywords can also utilize the OVERLAY keyword to specify a starting position.

12. Explain how you would use the QCMDEXC API to run CL commands from an RPGLE program.

To use the QCMDEXC API to execute CL commands from an RPGLE program, you would first need to declare the API in your RPGLE program as an external procedure. The prototype involves specifying the API name (QCMDEXC), parameters for the command string and its length. Then, you'd call the QCMDEXC API, passing the CL command you want to execute as a string and the length of that string. The API then executes the CL command.

For Example:

D Qcmdexc        PR              ExtProc('QCMDEXC')
D  command                    32766A   Const Varying
D  command_length                 15P 5 Const

C                   Eval      command = 'CRTLIB MYLIB'
C                   Eval      command_length = %len(command)
C                   CallP     Qcmdexc(command : command_length)

13. How do you handle date and time data types effectively in RPGLE?

In RPGLE, date and time data types are handled using the *ISO (YYYY-MM-DD), *USA (MM/DD/YYYY), *EUR (DD.MM.YYYY), *JIS (YYYY/MM/DD) date formats, along with corresponding time formats like *ISO (HH.MM.SS). You can define date/time fields using the D (date), T (time), and Z (timestamp) data types in your D-specs. Built-in functions like %DATE, %TIME, %TIMESTAMP, %CHAR, %DEC, %INT, %TIMESTAMP, EXTEND and operators such as + and - are used for date/time arithmetic and conversion. It is critical to use a consistent date/time format for database fields and calculations to avoid errors. For example:

D dateField        D   DATE(*ISO)
D timeField        D   TIME(*ISO)
D timestampField   D   TIMESTAMP

C                   EVAL      dateField = %DATE()
C                   EVAL      timeField = %TIME()
C                   EVAL      timestampField = %TIMESTAMP()

When working with external data or legacy systems that use different date/time formats, ensure to convert the data into RPGLE's native formats or a common intermediate format (like timestamp) during data exchange. %TIMESTAMP is often a good interchange format because it is a single field that contains both date and time information.

14. What are the benefits of using qualified data structures in RPGLE?

Qualified data structures in RPGLE offer several benefits, primarily related to code organization and readability. By qualifying subfields, you can create more descriptive and maintainable code. This reduces ambiguity, especially when dealing with multiple data structures containing identically named subfields. Imagine having two data structures, Customer and Employee, both with a Name subfield. Without qualification, referencing Name would be ambiguous; with qualification (e.g., Customer.Name, Employee.Name), the code becomes much clearer.

Furthermore, qualified data structures simplify array handling within data structures. You can define arrays of subfields easily, allowing for structured and efficient data manipulation. They also enhance the ability to pass complex data as parameters between procedures, improving modularity. Using qualified data structures often leads to cleaner and more maintainable RPGLE code, ultimately reducing debugging time and improving overall code quality.

15. Describe a scenario where you would use the EVAL-CORR operation in RPGLE.

I would use the EVAL-CORR operation in RPGLE when I need to move data between two data structures that have some similarly named subfields, but not all subfields are identical, and the layout may not be exactly the same. For example, imagine I'm moving data from an externally described file's record format into a work data structure for processing.

Specifically, if both data structures contain a 'CUSTOMER_ID' field, EVAL-CORR will automatically move the value of 'CUSTOMER_ID' from the source to the target. If the target does not have a matching field, nothing happens. This simplifies the code compared to manually moving each common field, especially when dealing with large data structures.

16. How can you dynamically allocate memory in RPGLE using the ALLOC and DEALLOC operations?

In RPGLE, dynamic memory allocation is achieved using the ALLOC and DEALLOC operations.

ALLOC is used to allocate a block of memory at runtime. You specify the size of the memory block to allocate, and ALLOC returns a pointer to the beginning of the allocated memory. You can then use this pointer to access and manipulate the data in the allocated memory. DEALLOC is used to release the dynamically allocated memory that was previously allocated using ALLOC. It's crucial to DEALLOC memory when it's no longer needed to prevent memory leaks. You pass the pointer to the DEALLOC operation, and it releases the memory block. For Example:

     D Ptr             S               *   INZ(*NULL)
     D Size            S             10I 0   INZ(1024) // Size in bytes

     // Allocate memory
     ALLOC %SIZE(Size) Ptr
     IF %ERROR();
       // Handle allocation error
       RETURN;
     ENDIF;

     // Use the memory (e.g., copy data into it)
     // ...

     // Deallocate the memory when finished
     DEALLOC Ptr;
     Ptr = *NULL;

17. Explain the concept of a control break report and how you would implement it in RPGLE.

A control break report is a report where the data is grouped and summarized based on changes in a specific field (the control field). When the value of the control field changes (a 'break' occurs), a summary section is printed for the previous group before printing the details of the new group.

In RPGLE, you'd implement this by sorting the input data by the control field. Then, in your RPGLE program's main loop, you would compare the current record's control field value to the previous record's value. If they differ, trigger a subroutine to print the summary information (totals, averages, etc.) for the previous group. After printing the summary, you'd reset the summary variables. The code would look something like this (psuedo code):

Read record.
Prev_Control_Field = Control_Field. 

Dow not *EOF;
   If Control_Field <> Prev_Control_Field; 
       Call Subroutine to print Summary of previous Control_Field. 
       Reset summary variables. 
   EndIf;

   Process current record. 
   Add record values to summary variables.
   Prev_Control_Field = Control_Field. 
   Read record.
EndDo;

18. What is the purpose of the MONITOR group in RPGLE exception handling?

The MONITOR group in RPGLE exception handling is used to enclose a block of code that you want to monitor for exceptions (errors). It's analogous to a try block in other languages like Java or C#.

If an exception occurs within the MONITOR block, the program control is transferred to the corresponding ON-ERROR block that matches the exception code (or a more general ON-ERROR block if a specific match isn't found). This allows you to handle errors gracefully without the program terminating abruptly. The general format is:

MONITOR;
   // Code to be monitored
ON-ERROR *ALL; // Or specific error codes like *FILE
   // Error handling code
ENDMON;

19. How do you use the %SUBST built-in function to extract a portion of a string in RPGLE?

The %SUBST built-in function (BIF) in RPGLE is used to extract a substring from a string. It takes three arguments:

%SUBST(string:start:length)

• string: The source string from which you want to extract the substring.
• start: The starting position of the substring (1-based index).
• length: The length of the substring to extract.

For example, to extract the characters from position 5 for a length of 3 from the string 'ABCDEFGHIJ', you would use: %SUBST('ABCDEFGHIJ':5:3) which would return 'EFG'.

20. Describe how you would convert a DDS-defined file to a DDL-defined table and the considerations involved.

Converting DDS (Data Description Specifications) to DDL (Data Definition Language) involves understanding the DDS file's structure and mapping it to equivalent DDL statements. You'd typically extract field names, data types, and lengths from the DDS. For example, a DDS definition like A R CUSTMAST CUSTOMER MASTER and A CUSNUM 6S 0 (CUSNUM is a 6-digit numeric field) would be translated into DDL such as CREATE TABLE CUSTMAST (CUSNUM INT);. Considerations include data type mapping (e.g., packed decimal in DDS to DECIMAL in SQL), handling key fields (defining primary keys in DDL), dealing with nullability (specifying NOT NULL or NULL constraints), and managing indexes (creating indexes in DDL based on DDS specifications). Also, you may need to address character encoding differences and collation settings during the conversion. The mapping process can be automated through custom scripts or utilize commercially available DDS conversion tools to streamline the process.

21. Explain how you can improve the performance of RPGLE programs when working with large datasets.

To improve RPGLE program performance when working with large datasets, consider these strategies. Optimize database access by using indexed access paths (SETLL, READE) instead of full table scans (READ). Use commitment control to minimize the impact of errors and improve transaction handling. For very large files, consider using embedded SQL for more direct control over data access. Avoid using %SUBST or other string manipulation operations in WHERE clauses as they can prevent index usage.

Other techniques include using data structures and arrays to hold frequently accessed data in memory, reducing I/O operations. Consider blocking factors when reading data into variables and use optimized built-in functions (BIFs) and SQL scalar functions whenever possible. Finally, analyze the program's execution using tools like Visual Explain in IBM i Access Client Solutions (ACS) to identify performance bottlenecks. Using compile time constants and avoiding redundant calculations can also improve program efficiency.

22. What is the difference between a shared and unshared lock in RPGLE database operations?

In RPGLE database operations, a shared lock (also known as a read lock) allows multiple programs to read the same record simultaneously. It prevents any program from acquiring an exclusive lock on that record, thus ensuring data consistency during read operations. Multiple programs can hold shared locks on the same record concurrently.

An exclusive (or unshared) lock, on the other hand, prevents any other program from accessing the record, either for reading or writing. When a program obtains an exclusive lock, it's the only program that can access the record until the lock is released. This is crucial for update operations to prevent data corruption or race conditions. UPDATELOCK keyword acquires an unshared lock on the record.

23. How would you use the SQL precompiler in RPGLE to prepare and execute SQL statements?

To use the SQL precompiler in RPGLE, you embed SQL statements directly within your RPGLE source code. These SQL statements are prefixed with EXEC SQL. The precompiler then translates these embedded SQL statements into equivalent RPGLE code that interacts with the database.

Specifically, you'd use EXEC SQL followed by the desired SQL statement (e.g., SELECT, INSERT, UPDATE, DELETE). For example:

     EXEC SQL SELECT col1 INTO :my_variable FROM my_table WHERE col2 = :some_value;

During compilation, the precompiler replaces this with RPGLE code to prepare, execute, and handle any results or errors. You must bind the program to the appropriate SQL service program (e.g., QSQCLI) to enable database interaction.

24. Describe the use of the EXFMT opcode in RPGLE.

The EXFMT opcode in RPGLE (Extended Format) is used to write a record format to a display device, and then read a record format from the same device. It's essentially a combined WRITE and READ operation. The primary purpose is to simplify the interaction with display files, allowing a single instruction to handle both displaying information and receiving input from the user. It uses the record format specified in the display file.

When using EXFMT, the program first writes the specified record format to the screen. The user then interacts with the displayed fields, modifies the input fields, and presses Enter (or a function key defined in the display file). The EXFMT opcode then reads the data entered by the user back into the input fields defined in the record format. After the EXFMT opcode is executed, the program can then process the user input stored in the input fields.

25. Explain the different types of file feedback areas available in RPGLE.

RPGLE provides several file feedback areas, primarily accessed through the INFDS (File Information Data Structure). The key ones are:

• File Feedback: This is the core feedback, populated after each I/O operation. It contains information such as record number, operation type, error codes, and file status. This is usually your primary source of file operation feedback.
• Open Feedback: This provides information related to the file's open state and attributes, like the file name, record length, and key field information. It's available after the file is opened. You generally use EXTFILE(*EXTDESC) with the OVRDBF command so it can obtain the right file attributes at compile and runtime.
• End of File (EOF) or Exception Feedback: This part contains specific information when an end-of-file or an exception/error occurs during file processing. Error codes are crucial for understanding what went wrong. For example, status code 1211 generally means record locked.

26. How would you use the CALLB operation code in RPGLE?

The CALLB operation code in RPGLE is used to call an external program or procedure bound by the binder. Unlike CALL, CALLB allows for passing parameters by reference or by value and can directly receive a return value. CALLB is useful for calling ILE procedures or programs that are not RPG.

Specifically, CALLB is beneficial when you need to call a procedure that returns a value, or when the called procedure requires parameters to be passed by value. For example:

CALLB(E) 'MYPROC' , PARM1 : PARM2 : RETVAL;

In this code MYPROC is the name of the procedure, PARM1 and PARM2 are input parameters, and RETVAL is the variable where the return value of MYPROC will be stored. The (E) indicates error handling. If an error occurs, the %ERROR built-in function will be set on, and the %STATUS built-in function can be examined for specific error codes.

27. Describe how you would implement a multi-threaded RPGLE program, and what are the potential challenges?

Implementing a multi-threaded RPGLE program involves using the _Racquire_MU and _Rrelease_MU built-in functions to manage access to shared resources. You would create a main RPGLE program that spawns multiple threads using the pthread_create API (accessed via a service program wrapper). Each thread executes a specific subroutine or procedure, potentially accessing shared data or I/O resources. Thread-safe data structures and synchronization mechanisms are essential.

Potential challenges include thread synchronization (avoiding race conditions, deadlocks), data consistency (ensuring all threads see a coherent view of shared data), debugging multi-threaded code, and proper error handling in a multi-threaded environment. You'd also need to be mindful of the limitations of RPGLE's threading model, such as the requirement to use _Racquire_MU and _Rrelease_MU for certain file operations and the fact that not all RPGLE built-in functions are thread-safe.

28. What are some strategies for debugging RPGLE programs, especially when dealing with complex logic or external calls?

Debugging RPGLE programs, especially with complex logic or external calls, requires a multi-faceted approach. Using the STRDBG command to start the debugger is fundamental. Within the debugger, set breakpoints at key locations to step through the code and examine variable values using commands like EVAL. For complex logic, utilize conditional breakpoints to halt execution only when specific criteria are met. When debugging external calls, inspect the parameters being passed and the return values to ensure proper communication.

Consider using display files to output the value of key variables during program execution. This is especially useful when debugging batch jobs or situations where interactive debugging is difficult. Additionally, review the job log for any error messages or exceptions that might provide clues to the problem. For very complex scenarios, consider using a source code management system to revert back to previous working versions of the code in order to narrow down when the error was introduced.

IBM RPG interview questions for experienced

1. How can you optimize RPG code for improved performance, specifically addressing issues like I/O operations and CPU usage?

Optimizing RPG code involves several key strategies. Minimize I/O operations by using techniques like blocking factors on files, using keyed access instead of full table scans, and utilizing embedded SQL for efficient data retrieval and manipulation. Reducing the number of reads and writes significantly improves performance.

To optimize CPU usage, focus on efficient coding practices. Use built-in functions where possible, avoid unnecessary loops, and consider using array operations instead of processing data element by element. Review the logic and algorithms used to ensure they are as efficient as possible. For example, instead of looping through a file to find a record, consider using SQL with a where clause on the key. Utilize compiler directives (e.g., OPTIMIZE(*FULL)) and profile the code to identify bottlenecks, then target those specific areas for optimization. Also, consider using the latest version of the RPG compiler to benefit from performance enhancements.

2. Describe your experience with embedded SQL in RPG programs. How have you used it to interact with databases, and what are some best practices?

I've used embedded SQL extensively in RPG programs to interact with DB2 databases on IBM i systems. I typically use it for data retrieval, insertion, updating, and deletion. For example, I would use EXEC SQL SELECT to retrieve data into RPG variables, EXEC SQL INSERT to add new records, EXEC SQL UPDATE to modify existing records, and EXEC SQL DELETE to remove records. I also frequently use host variables to pass data between the RPG program and the SQL statements.

Some best practices I follow include using parameter markers (?) instead of hardcoding values in SQL statements to prevent SQL injection and improve performance. I also utilize commitment control (*NONE, *CHG, *CS) to ensure data integrity and handle errors gracefully using SQLCODE and SQLSTATE to check the outcome of SQL operations. Moreover, I strive to optimize SQL queries by creating indexes and analyzing query performance with tools like Visual Explain. Finally, I always use EXEC SQL INCLUDE SQLCA to declare the SQLCA data structure.

3. Explain the concept of service programs in RPG. How do they promote code reusability, and what are the advantages of using them?

Service programs in RPG are compiled modules that contain procedures or functions that can be called by other RPG programs or service programs. They are similar to DLLs or shared libraries in other languages. The primary goal of service programs is to promote code reusability. Instead of duplicating the same code in multiple programs, you can create a service program with the common routines and then call those routines from any program that needs them.

Advantages of using service programs include:

• Code Reusability: Avoid code duplication, making maintenance easier.
• Modular Design: Promotes a modular approach to development, breaking down large applications into smaller, manageable units.
• Improved Maintainability: Changes to a service program only need to be made in one place, rather than in multiple programs.
• Reduced Compilation Time: Programs that use service programs compile faster because the common code is already compiled and linked in the service program.
• Encapsulation: Service programs can encapsulate complex logic or data access, simplifying the calling programs.
• Example: Create Service program ```rpgle H DFTACTGRP(*NO) ACTGRP(*CALLER)

P GetNextOrder PI 10I 0 D OrderNum 10I 0

/free //Logic to retrieve next order number from a file or database. OrderNum = 12345; return OrderNum; /end-free

*   **Example: Call Service program**
```rpgle
     /copy prototypes,GetNextOrder.rpgle

D OrderNumber 10I 0

/free
   OrderNumber = GetNextOrder();
   dsply OrderNumber;
/end-free

4. What are the differences between commitment control and rollback processing in RPG, and when would you use each?

Commitment control and rollback processing in RPG are mechanisms for managing database transactions. Commitment control allows you to group a series of database operations into a single logical unit of work. Changes are only permanently applied to the database when the COMMIT operation is issued. If any part of the unit fails, a ROLLBACK operation can undo all the changes made within that unit, ensuring data consistency. You'd use commitment control when you need to ensure that multiple related database operations either all succeed or all fail as a single unit, such as transferring funds between accounts or processing an order.

Rollback processing, on the other hand, typically refers to the manual handling of errors within a program without the formal structure of commitment control. While you might implement your own error handling and data restoration logic using RPG code, it doesn't provide the same level of database-managed transaction integrity as commitment control. For example, if a file update fails you may write code to restore the original value. Rollback processing is used in legacy environments or when full commitment control is not necessary (e.g., single file updates or simple data modifications) or feasible (due to platform/database limitations).

5. Discuss your experience with debugging RPG programs. What tools and techniques do you find most effective for identifying and resolving errors?

My experience debugging RPG programs includes utilizing several tools and techniques to effectively identify and resolve errors. I frequently use the STRDBG command (Start Debug) to step through the code, set breakpoints, and inspect variable values in real-time. This allows me to follow the program's logic and pinpoint exactly where deviations occur. I also use the DSPPGMVAR (Display Program Variable) command to examine the contents of variables at specific points in the code.

Beyond these commands, I find techniques such as reviewing the job log for error messages and creating test cases to reproduce the errors crucial. Analyzing the call stack and looking at the program's output often provide valuable clues. For complex issues, I might use the /FREE form of RPG to isolate sections of code to facilitate the debugging process. I also rely on the integrated debugger in Rational Developer for i (RDi) for a more visual and interactive debugging experience.

6. How have you used user interfaces with RPG, such as SDA or the web? What are the pros and cons of each approach?

I've used both SDA (System Display Architecture) interfaces and web-based interfaces with RPG. With SDA, I primarily built green-screen applications for internal business processes. The pros were rapid development within the IBM i environment and tight integration with DB2. Cons included a limited user experience compared to modern interfaces, the steeper learning curve for users accustomed to graphical interfaces, and limitations in UI customization.

For web-based interfaces, I've used technologies like Node.js and PHP to create front-ends that interact with RPG backends through APIs or services. The advantages here are a much richer user experience, cross-platform compatibility, and easier integration with other web-based systems. However, the development process can be more complex, requiring expertise in multiple technologies, and there can be challenges in ensuring secure communication and data transfer between the web server and the IBM i system.

7. Explain the purpose of control language (CL) programs and how they interact with RPG programs.

CL programs (Control Language programs) on IBM i (AS/400) serve as the operating system's scripting language. Their primary purpose is to control jobs, manage system resources, and automate operations. They act as an interface between the user or system and the operating system. Common tasks include starting subsystems, managing batch jobs, handling error conditions, and performing system administration tasks.

CL programs interact with RPG programs in several ways. CL can call RPG programs (and vice versa). CL programs commonly use the CALL command to execute an RPG program, passing parameters if needed. RPG programs can also use the CALL opcode to execute CL programs. The interaction allows for separating system control logic (in CL) from application logic (in RPG), promoting modularity and maintainability. For example, a CL program might handle user authentication and then call an RPG program to process a transaction. Additionally, CL programs can process the return codes from RPG programs to determine the next action.

8. What are the different ways to handle errors and exceptions in RPG programs, and what are the best practices for error handling?

RPG provides several mechanisms for handling errors and exceptions. These include: Status codes (%STATUS): Checking the %STATUS built-in function after each operation to determine if an error occurred. This is the most basic approach. Error indicators: Using error indicators (specified in positions 73-74 of the DDS or calculation specifications) to branch to error handling routines when an error occurs. MONITOR groups: Using MONITOR, ON-ERROR, and ENDMON blocks to handle exceptions similar to try-catch blocks in other languages. *PSSR subroutine is a program status subroutine which is invoked when unhandled exceptions occur.

Best practices involve using MONITOR groups for structured exception handling, especially for I/O operations or calls to external procedures. Always check %STATUS after operations that might fail. Implement a *PSSR subroutine for handling unexpected exceptions and logging errors. Always log errors with sufficient details for debugging and include error codes or messages. Avoid using error indicators for new development, favor %STATUS and MONITOR groups.

9. Describe your experience with file handling in RPG, including different file types (e.g., physical files, logical files) and access methods.

In RPG, I've worked extensively with file handling, using both physical and logical files. Physical files store the actual data, while logical files provide different views or access paths to the same underlying physical data, often utilizing indexes. I've used various access methods, including sequential read (READ, READP), direct access using record numbers (READE, SETLL/READE) and keyed access for both reading and writing to the files, utilizing opcodes like READE, SETLL, CHAIN, WRITE, UPDATE, and DELETE.

I've also worked with different file definition specifications (F-specs) to declare the file type, record length, key fields, and other attributes. I am comfortable with handling file status codes and implementing error handling routines to ensure data integrity during file operations. Furthermore, I have experience using embedded SQL to access data, which offers another powerful way to interact with database files in RPG programs.

10. How do you handle date and time data in RPG programs, including formatting, calculations, and comparisons?

In RPG, date and time data are typically handled using data types like DATE, TIME, and TIMESTAMP. Formatting is done using the %CHAR built-in function, specifying a format like %CHAR(myDate : *ISO) or %CHAR(myTime : *HMS). Calculations can be performed using built-in functions like %DAYS, %MONTHS, and %YEARS to add or subtract intervals. Comparisons are straightforward using standard relational operators (>, <, =, etc.) directly on the date/time fields. For example:

IF Date1 > Date2; // Date1 is later than Date2 ENDIF;

Eval NewDate = Date1 + %DAYS(15);

These built-in functions and direct comparisons provide a relatively easy way to manage dates and times within RPG programs.

11. What are the advantages and disadvantages of using subfiles in RPG programs, and when would you use them?

Subfiles in RPG offer several advantages. They provide a user-friendly way to display and manipulate multiple records on a single screen, improving user experience. They simplify the display of data retrieved from database files and allow users to easily scroll through records. Subfiles also reduce I/O operations compared to reading and writing individual records, improving performance.

However, subfiles also have disadvantages. They can be more complex to code and debug than simpler display file designs. Managing the subfile's load and display logic requires careful attention. Performance can degrade with very large subfiles if not properly optimized. You would typically use subfiles when you need to present a list of records for browsing, selection, or editing, such as displaying a list of customers, products, or orders. They are particularly useful when the user needs to interact with multiple records at once.

12. Discuss your experience with data queues in RPG programs. How have you used them for inter-program communication?

I've used data queues extensively in RPG programs for asynchronous inter-program communication. Specifically, I have leveraged them to decouple processes, improving the overall resilience and responsiveness of applications. For instance, in an order processing system, the front-end order entry program puts order details onto a data queue. A separate back-end program, running independently, retrieves and processes the orders from the queue. This prevents the front-end from being blocked by potentially slow order processing tasks.

I've also used data queues for implementing a producer-consumer pattern in several applications. For example, consider a scenario where a program generates reports periodically and another program needs to email those reports. The program generating reports puts the report information (e.g., path, recipients) onto a queue, and the email sending program retrieves the info from the queue and sends the report. I've used opcode such as QSNDDTAQ to send data and QRCVDTAQ to receive data from the queue. Using data queues this way allows me to create a more modular and scalable application.

13. Explain the concept of data areas in RPG and how they can be used to share data between programs.

Data areas in RPG are named storage locations that can be accessed by multiple RPG programs. They provide a mechanism for sharing data between programs without using files or parameters. Data areas are created and managed using RPG commands like CRTDTAARA, CHGDTAARA, RTVDTAARA, and DLTDTAARA. They can be defined as character, decimal, or logical types and are stored in a library. They are used to maintain common values across programs or provide a simple inter-program communication method.

To share data, one program updates the data area using CHGDTAARA, and another program retrieves the updated value using RTVDTAARA. This allows programs to communicate and share information easily. For example:

//Program 1 (updates the data area)
CHGDTAARA DTAARA(MYLIB/MYDTAARA) VALUE('Updated Value')

//Program 2 (retrieves the data area)
RTVDTAARA DTAARA(MYLIB/MYDTAARA) RTNVAR(&MyVariable)
DSPLY &MyVariable

14. How do you implement security measures in RPG programs to protect sensitive data and prevent unauthorized access?

RPG programs can implement security measures through several methods. Data level security can be enforced using authority checking at the file and field level. Objects such as files, programs, and commands are secured using object level security which includes public (*PUBLIC) and private authorities. You can use CHGAUT (Change Authority) command to grant specific permissions (e.g., *USE, *CHANGE, *EXCLUDE) to users or groups for these objects. Adopted authority allows a program to run under the authority of the program owner rather than the user running it. Input validation should be implemented to prevent SQL injection or buffer overflows. CL commands can be secured using the SECCMD system value. Proper authorization lists can be implemented to further restrict access to objects.

15. What are the different ways to call RPG programs from other programming languages or systems, such as Java or web applications?

RPG programs can be invoked from other languages and systems through several methods. One common way is using IBM i Services, which expose RPG functionality as callable procedures or functions. These services can then be accessed using standard protocols like ODBC, JDBC, or web services (SOAP/REST).

Another option is to use ILE (Integrated Language Environment) concepts to create service programs containing RPG procedures. These service programs can then be called from other ILE languages like Java or C++ using procedure pointers or similar mechanisms. Additionally, tools such as IBM Toolbox for Java can be utilized to directly call RPG programs from Java applications. This involves creating Java classes that interact with the RPG program through remote command execution or data queue interfaces.

For web applications, solutions involve using an HTTP API that invokes a web service to trigger an RPG program via a job queue.

16. Describe your experience with performance tuning RPG programs. What are some common performance bottlenecks, and how do you address them?

I have experience tuning RPG programs on IBM i. Common performance bottlenecks often stem from inefficient database access, especially un-indexed or poorly indexed fields in SELECT, JOIN, and WHERE clauses. For example, full table scans can be very slow. I address this by analyzing query plans (using Visual Explain or STRDBMON) to identify slow performing SQL statements, then work with database administrators to create or modify indexes. Another area is using appropriate data structures within the RPG code itself. Using arrays or data structures for frequent lookups can be faster than repeated reads from a database table. Other times, it is beneficial to replace complex calculations within RPG code with equivalent SQL to leverage DB2's optimized query engine, or rewrite complex logic to simpler and direct statements. Also, avoid embedded SQL and use native I/O operations if possible, where appropriate.

Additionally, I've addressed bottlenecks caused by inefficient looping structures or redundant calculations within RPG code. Specifically, ensure to minimize I/O within loops and optimize array processing by considering blocking factors. Finally, I monitor the jobs (using WRKACTJOB) to understand resource utilization of each job and identify any high CPU jobs for code review.

17. How do you approach code maintenance and refactoring in RPG programs to improve readability, maintainability, and performance?

Code maintenance and refactoring in RPG involves several key steps. First, thorough analysis of the existing code is essential, often using tools to identify areas of complexity, redundancy, or performance bottlenecks. We can improve readability by applying consistent formatting, meaningful variable names, and clear comments explaining complex logic.

Refactoring techniques include breaking down large subroutines into smaller, more manageable functions, using modern RPG features like free-format and data structures, and eliminating redundant code through techniques like creating reusable modules or service programs. Performance improvements often involve optimizing I/O operations, leveraging SQL when appropriate, and carefully profiling code to pinpoint areas for optimization. Regular code reviews and unit testing are crucial throughout the process to ensure that changes do not introduce new issues and that the system continues to work as expected.

For example, a large, monolithic subroutine performing multiple tasks can be refactored into separate, well-defined procedures. Legacy code can be updated to utilize features like SQLRPGLE or JSON parsing to replace older, less efficient methods. Regularly using tools such as IBM Rational Developer for i can assist in code analysis and refactoring.

18. What are the different types of locking mechanisms available in RPG, and how do you use them to prevent data corruption in multi-user environments?

RPG provides several locking mechanisms to prevent data corruption in multi-user environments. The primary locking methods are record-level locking and file-level locking. Record-level locking, achieved using the *EXCLRD (exclusive read), *EXCL (exclusive), *SHRRD (shared read) keywords in the file definition or via op-codes like READE, READP, and UPDATE, locks specific records. This is the most common and efficient approach. File-level locking, using the *EXCLRD or *EXCL attributes when opening the file, locks the entire file, preventing other programs from accessing it; this is generally used for batch processes or when a program needs exclusive access to a file for a short period.

To use these locks, you specify the lock type in the file declaration using the USROPN keyword (allowing explicit open) or implicitly through the op-codes. For example, when using the UPDATE opcode, the record being updated is automatically locked. When a program attempts to access a locked record or file, it will wait until the lock is released or an error condition is raised based on the system settings and the program's error handling. Properly handling lock contention and potential deadlocks (where multiple programs are waiting for each other to release locks) is crucial for ensuring data integrity.

19. Explain the concept of journaling in RPG and how it can be used to recover data in the event of a system failure.

Journaling in RPG involves recording changes made to database files in a journal receiver. This receiver acts as a log, capturing before and after images of records modified by RPG programs. Should a system failure occur, the journal can be applied to the database files to roll forward or roll back transactions, ensuring data consistency.

Recovery uses the Apply Journaled Changes (APYJRNCHG) command. This command uses the information in the journal receiver to either:

• Roll forward: apply changes that were committed but not yet physically written to the database files.
• Roll back: undo changes made by transactions that were in progress but not committed at the time of the failure.

The journal entries contain the necessary information, such as the file name, record ID, and the data before and after the change, enabling accurate data recovery.

20. How do you use compiler directives and conditional compilation in RPG programs to customize code behavior based on different environments or configurations?

Compiler directives in RPG, such as /DEFINE, /IF, /ELSEIF, /ELSE, and /ENDIF, allow for conditional compilation. You can define different variables for different environments (e.g., DEBUG, PRODUCTION) using /DEFINE. Then, using /IF and related directives, you conditionally include or exclude blocks of code based on whether a particular variable is defined.

For example:

     /DEFINE DEBUG

     /IF DEFINED(DEBUG)
      // Debugging code, e.g., display variable values
      dsply 'Debugging mode active!';
     /ELSE
      // Production code
      callp PerformImportantTask();
     /ENDIF

This lets you include debug code in a development or test environment while excluding it in production, controlling behavior based on the compilation environment.

21. Discuss your experience with integrating RPG programs with other systems or applications, such as web services or APIs.

My experience with integrating RPG programs primarily involves using web services and APIs. I've utilized the HTTPAPI library extensively to consume external web services from RPG programs. This included crafting HTTP requests (GET, POST, PUT, DELETE) and parsing JSON or XML responses to extract relevant data for use within RPG applications. I've also written RPG programs that expose functionality as web services using technologies like CGI and more recently, ILE procedures combined with JSON serialization/deserialization libraries to create RESTful APIs. For example:

// Example using HTTPAPI to call a web service
exec sql set :url = 'https://api.example.com/data';
rc = HTTP_GET(url : %addr(response) : %len(response));
// Then parse the response (assuming JSON) with a JSON parser library

I have also worked on integrating RPG programs with other internal systems using technologies like data queues and database links (DBCS). Security considerations, especially authentication and authorization when dealing with external APIs, have always been a priority during these integration projects.

22. How do you use the SQL precompiler in RPG programs to optimize SQL statements and improve performance?

The SQL precompiler in RPG programs optimizes SQL statements by translating embedded SQL code into native RPG code. This process involves several steps:

1. Syntax Checking: The precompiler first validates the SQL syntax for errors. It ensures that the SQL statements are correctly formed and that the database objects (tables, views, etc.) exist.
2. Translation: Valid SQL statements are translated into RPG code. This typically involves calls to SQL APIs (e.g., SQLEXEC, SQLPREP, SQLOPEN, SQLFETCH). The precompiler handles the complexities of interfacing between RPG and the database system.
3. Optimization: During precompilation, the database optimizer can be invoked. This allows the database to determine the most efficient execution plan for the SQL statement before runtime. This can lead to significant performance improvements.
4. Creation of Access Paths: In some cases, the precompiler can create access paths (indexes) if they don't exist. This improves performance if the SQL statement uses these access paths.
5. Code Generation: Finally, the precompiler generates RPG source code that includes the translated SQL statements along with the necessary database interaction logic. This RPG source is then compiled into an executable program. Using the precompiler allows for better error detection and potentially improved execution plans, ultimately enhancing performance compared to dynamic SQL.

23. What are the different ways to handle large objects (LOBs) in RPG programs, such as images or documents?

RPG provides several ways to handle Large Objects (LOBs) like images or documents. You can use BLOBs (Binary Large Objects) or CLOBs (Character Large Objects). BLOBs are for binary data, while CLOBs are for character data. You can define LOB fields in database tables and use SQL statements to retrieve and update them. RPG provides built-in functions and APIs to work with LOB data, such as %SUBST for extracting parts of CLOBs, and APIs to read/write LOB data in chunks, which is essential for handling very large objects efficiently.

Alternatively, the Integrated File System (IFS) can be used. The file can be saved into IFS and the RPG code can store the IFS path. Data can be read/written using IFS APIs. Using SQL to manage LOBs is usually preferable, but the IFS approach might be necessary in specific circumstances.

24. Explain the concept of user-defined functions (UDFs) in RPG and how they can be used to extend the functionality of the language.

User-defined functions (UDFs) in RPG allow developers to create custom functions that can be called like built-in RPG functions. This extends the language's capabilities by encapsulating reusable logic into modular units. UDFs improve code readability and maintainability by breaking down complex tasks into smaller, manageable functions.

UDFs are defined using the **FREE form and the Procedure keyword. They can accept parameters and return values. For example:

 dcl-proc MyUDF; 
  dcl-pi MyUDF packed(5:0);
   input parm packed(5:0) const; 
  end-pi; 
  return input * 2;
 end-proc;

This function can be called within RPG code like any other built-in function: result = MyUDF(my_value);

25. How do you use the Integrated Language Environment (ILE) in RPG programs to take advantage of modern programming techniques and features?

ILE in RPG allows modular programming and code reuse. I leverage ILE by creating modules with specific functionalities (e.g., data validation, database access). These modules are then bound together into a program. This promotes code organization, testability, and maintainability.

Key ILE features I utilize include:

• Procedures: Replacing monolithic programs with smaller, reusable procedures.
• Modules: Grouping related procedures and data definitions into logical units.
• Service Programs: Creating reusable libraries of procedures that can be shared across multiple applications.
• Activation Groups: Controlling the lifecycle and resource management of programs and modules. Activation groups help avoid conflicts when calling RPG programs from other languages or vice versa.

For example, I might create a service program MYLIB/STRINGUTIL with procedures for string manipulation. This service program can then be used by multiple RPG programs. When calling other languages like C or Java, I can pass parameters effectively. I also use features like *INLR = *OFF to control program termination, and leverage debugger improvements that ILE provides.

IBM RPG MCQ

Which IBM RPG skills should you evaluate during the interview phase?

While a single interview can't reveal everything about a candidate, focusing on key skills is important. For IBM RPG roles, certain skills are more predictive of success than others. Identifying these skills helps you make informed hiring decisions.

RPG Programming Fundamentals

Testing RPG programming fundamentals using MCQs can help filter candidates rapidly. Adaface's IBM RPG assessment includes relevant questions to evaluate this skill.

Ask targeted interview questions to assess the candidate's grasp of RPG fundamentals. This will supplement the multiple choice questions.

Explain the difference between fixed-form and free-form RPG.

Look for an understanding of the historical context of fixed-form RPG and the advantages of free-form RPG. The ability to explain the benefits of modern RPG syntax suggests a willingness to learn and adapt.

DB2 Database Interaction

Skills in DB2 database interaction are tested on Adaface using our IBM DB2 online test. You can also assess if they know how to write queries, manipulate and retrieve data.

Prepare questions focused on using SQL within RPG programs. Understand their familiarity with handling database operations.

Describe how you would embed an SQL statement within an RPG program to retrieve data from a table.

The ideal response should cover the use of embedded SQL syntax (e.g., EXEC SQL), host variables, and error handling. The ability to explain the process indicates practical experience with DB2 integration.

IBM i (AS/400) Environment

Assessing knowledge of the IBM i environment with MCQs provides a holistic view of a candidate's skills. Consider using a technical aptitude test to check a candidate's comfort with navigating new environments.

Probe their experience with IBM i system administration tasks. This would test their competence to navigate the environment.

How would you check the status of a job running on the IBM i system?

Look for familiarity with commands like WRKACTJOB and the ability to interpret job status information. Knowledge of IBM i system commands shows practical experience with the platform.

3 Tips for Using IBM RPG Interview Questions

You've reached the end of this comprehensive guide! Before you start using these IBM RPG interview questions, here are three tips to help you conduct more successful interviews and hire the best talent.

1. Leverage Skills Assessments to Streamline Candidate Evaluation

Before diving into interviews, use skills assessments to filter candidates. This helps identify those with the strongest practical knowledge of IBM RPG, saving you valuable time and resources.

Adaface offers a range of assessments that can significantly improve your screening process. Consider using our IBM DB2 online test to evaluate database skills or a more general programming test to gauge overall coding ability. This allows you to focus on candidates who have demonstrated a baseline proficiency.

Implementing these assessments allows you to quickly identify candidates who are truly prepared for the role. This approach ensures that interview time is spent with the most promising individuals, leading to a more effective hiring process.

2. Curate a Focused Set of Interview Questions

Time is limited in interviews. Select a concise and pertinent set of questions to extract the most valuable information about a candidate's abilities and experience. A focused approach ensures you cover the most critical aspects of the role.

To complement your IBM RPG questions, consider adding questions to assess related database skills or system knowledge. You might find valuable questions on pages like our SQL Interview Questions or even DB2 interview questions.

Carefully chosen questions maximize your ability to evaluate candidates on relevant fronts, significantly increasing your chances of hiring a suitable candidate.

3. Master the Art of Follow-Up Questions

Simply asking interview questions is not enough. Asking effective follow-up questions is key to uncovering the depth of a candidate's knowledge and experience. It helps you differentiate between superficial understanding and genuine expertise.

For example, if a candidate describes a method for handling file I/O in RPG, a good follow-up might be: "What are the potential drawbacks of this approach in a multi-user environment, and how would you mitigate them?" This reveals whether the candidate has truly mastered the topic, or if their knowledge is limited.

Hire Talented RPG Developers with Skills Tests

If you're aiming to hire RPG developers, accurately assessing their skills is key. The most effective approach is to utilize skills tests. Consider leveraging our IBM DB2 Online Test to evaluate candidates' abilities.

Once you've identified top performers through skills tests, shortlist them for interviews. Ready to take the next step? Sign up on Adaface to streamline your hiring process.

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