Expressions and Assignment in RPGLE

Learning Objective

By the end of this lesson, you will be able to read and write simple RPGLE assignment statements, and recognize common arithmetic and comparison operators used in expressions.

Simple Explanation

You have already seen simple assignment statements, such as custName = 'Jordan Lee';, in earlier lessons in this group. This lesson looks more closely at assignment itself, and at expressions: the combinations of values, variables, and operators that produce a result.

In free-format RPGLE, assignment is written simply as a variable name, followed by an equals sign, followed by an expression:

dcl-s orderTotal packed(9:2);
dcl-s discountPct packed(3:0);
dcl-s finalTotal packed(9:2);

orderTotal = 100.00;
discountPct = 10;
finalTotal = orderTotal - (orderTotal * discountPct / 100);

Common arithmetic operators used in RPGLE expressions include + (addition), - (subtraction), * (multiplication), and / (division). RPGLE also supports comparison operators, commonly used together with the conditional logic covered in the next lesson, including = (equal to), <> (not equal to), < (less than), > (greater than), <= (less than or equal to), and >= (greater than or equal to).

An expression can be as simple as a single literal or variable, or can combine several values and operators together, as shown in the finalTotal calculation above, which combines subtraction, multiplication, and division into a single expression.

Why It Matters

Assignment and expressions are how an RPGLE program actually calculates and updates the values it works with. Nearly every meaningful piece of business logic, applying a discount, totaling an order, checking whether a value falls within an allowed range, depends on correctly written expressions and assignment statements. This makes them one of the most fundamental, frequently used building blocks in any RPGLE program.

Practical Example

Imagine a program calculating a final order total after a discount, as shown in the example above. Reading the expression orderTotal - (orderTotal * discountPct / 100) step by step: first, orderTotal * discountPct / 100 calculates the discount amount, and then that discount amount is subtracted from orderTotal to produce the final total.

Being able to read an expression like this piece by piece, rather than all at once, makes even a somewhat complex calculation approachable. This is a simplified, illustrative example rather than a specific real order calculation, but it reflects a genuinely common pattern in RPGLE business logic.

Common Confusions

"Does the equals sign in an assignment statement mean the same thing as in a math class?" Not exactly. In an assignment statement like finalTotal = orderTotal;, the equals sign means "store the value on the right into the variable on the left," rather than stating that two things are already equal to each other.

"Is = used for both assignment and comparison in RPGLE?" Yes, context tells them apart. Used in an assignment statement on its own, like discountPct = 10;, = assigns a value. Used inside a condition, as covered in the next lesson, = compares two values instead.

"Do I need parentheses in every expression?" No. Parentheses are useful for making the order of operations clear, especially in expressions combining more than one operator, as in the finalTotal example. Simple expressions with only one operator often do not need them.

Quick Recap

• Assignment in free-format RPGLE is written as a variable name, an equals sign, and an expression.
• Common arithmetic operators include +, -, *, and /; common comparison operators include =, <>, <, >, <=, and >=.
• An expression can combine multiple values and operators, and parentheses help make the order of operations clear.
• The equals sign means different things depending on context: assignment on its own, or comparison inside a condition.

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 divide by zero in an RPGLE expression?"
• "How does RPGLE decide the order to calculate an expression with more than one operator?"