Constants and Literals in RPGLE

Learning Objective

By the end of this lesson, you will understand what a literal value is, what an RPGLE constant is, and why using a named constant is often better than repeating the same literal value throughout a program.

Simple Explanation

In the Variables and Data Types in RPGLE lesson, you saw an assignment like custName = 'Jordan Lee';. The value 'Jordan Lee' written directly into that line of code is called a literal: a fixed value typed directly into the program, rather than stored in a variable.

RPGLE supports different kinds of literals matching the data types you already know:

• Character literals, written inside single quotes, such as 'Jordan Lee'.
• Numeric literals, written as plain numbers, such as 100 or 19.99.
• Indicator literals, *on and *off, representing the two possible values of an indicator variable.

A constant is a named value, declared once using dcl-c (Declare Constant), that behaves like a variable in that it has a name, but, unlike a regular variable, its value cannot be changed after it is declared:

dcl-c MAX_DISCOUNT_PCT 20;

dcl-s discountPct packed(3:0);
discountPct = MAX_DISCOUNT_PCT;

Using a named constant instead of repeating the same literal value throughout a program means that if that value ever needs to change, it only needs to be updated in one place, the constant's declaration, rather than everywhere it was typed directly into the code.

Why It Matters

Recognizing the difference between literals and constants, and knowing when to reach for a named constant, is a small but genuinely useful habit. Repeating the same literal value in many places throughout a program makes that value harder to find, easier to update inconsistently, and generally harder for someone else, or your future self, to understand why that specific value matters.

Practical Example

Imagine a program that applies a maximum discount percentage in several different places throughout its logic. If that percentage is typed directly as the literal 20 in five different spots, changing the business rule later means finding and updating all five, and easily missing one by mistake.

Declaring MAX_DISCOUNT_PCT as a constant once, and referring to it by name everywhere the value is needed, means a future change only requires updating that one declaration. This is a simplified, illustrative example rather than a specific real program, but it reflects a genuinely common, practical reason RPGLE developers use named constants.

Common Confusions

"Is a constant the same thing as a variable?" Not quite. Both have a name and a declared value, but a constant's value is fixed once declared and cannot be changed while the program runs, while a regular variable, declared with dcl-s, can be assigned new values as the program executes.

"Do I need to use dcl-c for every literal value in my program?" No. Small, one-off literal values used only in a single place, such as assigning a person's name in a simple example, are fine as plain literals. Named constants are most valuable for values that are meaningful, reused in multiple places, or likely to need updating later.

"Can a constant's value be calculated from other variables?" No, not in the simple sense covered in this lesson. A constant declared with dcl-c holds a fixed value known when the program is written, not a value calculated while the program runs.

Quick Recap

• A literal is a fixed value typed directly into RPGLE code, such as 'Jordan Lee', 100, or *on.
• A constant, declared with dcl-c, is a named value that cannot be changed after it is declared.
• Using named constants instead of repeated literals makes a program easier to update consistently and easier for others to understand.
• Constants are most valuable for meaningful values reused in more than one place.

Try Asking the AI Tutor

Use the AI Tutor to ask follow-up questions about this lesson. For example, try asking:

• "What happens if I try to change the value of a dcl-c constant while the program is running?"
• "What are some good examples of values that make sense as named constants?"