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Data Structures

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In this module, we will delve into the various data structures available in RPG programming. Understanding data structures is crucial for efficient data management and manipulation in your programs. We will cover the following topics:

  1. Introduction to Data Structures
  2. Defining Data Structures
  3. Using Data Structures
  4. Practical Examples
  5. Exercises

  1. Introduction to Data Structures

Data structures are a way of organizing and storing data so that it can be accessed and modified efficiently. In RPG, data structures are used to group related data items together, which can then be manipulated as a single entity.

Key Concepts:

  • Data Structure (DS): A collection of related data items.
  • Subfields: Individual elements within a data structure.
  • Qualified Data Structures: Data structures that allow subfields to be accessed using a qualified name.

  1. Defining Data Structures

In RPG, data structures are defined using the DCL-DS (Declare Data Structure) statement. Each subfield within the data structure is defined with its own data type and length.

Example:

DCL-DS Employee;
  EmpID      CHAR(5);
  FirstName  CHAR(20);
  LastName   CHAR(20);
  Salary     PACKED(7:2);
END-DS;

Explanation:

  • DCL-DS Employee; declares a data structure named Employee.
  • EmpID, FirstName, LastName, and Salary are subfields within the Employee data structure.
  • CHAR(5) specifies a character field with a length of 5.
  • PACKED(7:2) specifies a packed decimal field with 7 digits, 2 of which are decimal places.

  1. Using Data Structures

Once a data structure is defined, you can use it in your program to store and manipulate data. You can access individual subfields using the dot notation.

Example:

DCL-DS Employee;
  EmpID      CHAR(5);
  FirstName  CHAR(20);
  LastName   CHAR(20);
  Salary     PACKED(7:2);
END-DS;

Employee.EmpID = 'E1234';
Employee.FirstName = 'John';
Employee.LastName = 'Doe';
Employee.Salary = 55000.00;

DSPLY Employee.FirstName + ' ' + Employee.LastName;

Explanation:

  • The Employee data structure is populated with values.
  • DSPLY displays the full name of the employee.

  1. Practical Examples

Example 1: Nested Data Structures

You can define data structures within other data structures to represent more complex data.

DCL-DS Address;
  Street    CHAR(30);
  City      CHAR(20);
  ZipCode   CHAR(10);
END-DS;

DCL-DS Employee;
  EmpID      CHAR(5);
  FirstName  CHAR(20);
  LastName   CHAR(20);
  Salary     PACKED(7:2);
  HomeAddress Address;
END-DS;

Employee.HomeAddress.Street = '123 Main St';
Employee.HomeAddress.City = 'Anytown';
Employee.HomeAddress.ZipCode = '12345';

Example 2: Qualified Data Structures

Qualified data structures allow you to use the same subfield names in different data structures without conflict.

DCL-DS Employee QUALIFIED;
  EmpID      CHAR(5);
  Name       CHAR(20);
END-DS;

DCL-DS Department QUALIFIED;
  DeptID     CHAR(3);
  Name       CHAR(20);
END-DS;

Employee.Name = 'John Doe';
Department.Name = 'HR';

  1. Exercises

Exercise 1: Define and Use a Data Structure

Define a data structure named Product with the following subfields: ProductID (CHAR(10)), ProductName (CHAR(30)), and Price (PACKED(7:2)). Populate the data structure with sample data and display the product name and price.

Solution:

DCL-DS Product;
  ProductID    CHAR(10);
  ProductName  CHAR(30);
  Price        PACKED(7:2);
END-DS;

Product.ProductID = 'P1001';
Product.ProductName = 'Laptop';
Product.Price = 999.99;

DSPLY Product.ProductName + ' costs $' + %CHAR(Product.Price);

Exercise 2: Nested Data Structures

Define a nested data structure for an Order that includes an OrderID (CHAR(10)), OrderDate (CHAR(10)), and a nested Product data structure. Populate the data structure with sample data and display the order details.

Solution:

DCL-DS Product;
  ProductID    CHAR(10);
  ProductName  CHAR(30);
  Price        PACKED(7:2);
END-DS;

DCL-DS Order;
  OrderID      CHAR(10);
  OrderDate    CHAR(10);
  OrderedProduct Product;
END-DS;

Order.OrderID = 'O12345';
Order.OrderDate = '2023-10-01';
Order.OrderedProduct.ProductID = 'P1001';
Order.OrderedProduct.ProductName = 'Laptop';
Order.OrderedProduct.Price = 999.99;

DSPLY 'Order ID: ' + Order.OrderID;
DSPLY 'Order Date: ' + Order.OrderDate;
DSPLY 'Product: ' + Order.OrderedProduct.ProductName;
DSPLY 'Price: $' + %CHAR(Order.OrderedProduct.Price);

Conclusion

In this section, we explored the concept of data structures in RPG programming. We learned how to define and use data structures, including nested and qualified data structures. By practicing with the provided examples and exercises, you should now have a solid understanding of how to effectively use data structures in your RPG programs. In the next module, we will dive into arrays and lists, which are essential for handling collections of data.

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