SELECT / WHEN / OTHER in RPGLE

Learning Objective

By the end of this lesson, you will be able to read and write a simple select / when / other block in free-format RPGLE, and explain when it is a better fit than a long chain of elseif branches.

Simple Explanation

In the IF / ELSE in RPGLE lesson, you learned how elseif lets you check several conditions in sequence. When there are many possible conditions to check against the same value, RPGLE offers an alternative structure, select, that is often easier to read.

A simple select block looks like this:

dcl-s custTier char(1);
dcl-s discountPct packed(3:0);

custTier = 'G';

select;
  when custTier = 'P';
    discountPct = 15;
  when custTier = 'G';
    discountPct = 10;
  when custTier = 'S';
    discountPct = 5;
  other;
    discountPct = 0;
endsl;

A select block starts with select and ends with endsl. Each when checks its own condition, similar to a separate if, and other covers whatever case is left when none of the when conditions matched, similar in spirit to else in an if block. As with if / elseif, only the first matching branch runs, and the rest are skipped.

Why It Matters

select becomes especially useful once you are checking many possible values for essentially the same thing, such as a customer tier, a status code, or a category. Writing this kind of logic as a long chain of if / elseif branches works, but can become harder to read as the number of conditions grows. select groups these checks together in a way that is often clearer at a glance.

Practical Example

Imagine the customer tier example above being used to determine a discount percentage. For a customer tier of 'G', IBM i checks each when in order: custTier = 'P' is false, custTier = 'G' is true, so discountPct is set to 10, and the remaining when and other branches are skipped.

Written instead as a long chain of if / elseif branches checking the same custTier value repeatedly, the logic would work the same way, but can feel more repetitive to read. This is a simplified, illustrative example rather than a specific real tier system, but it reflects a genuinely common, practical reason RPGLE developers reach for select.

Common Confusions

"Is select just a different way to write the same thing as if / elseif?" In terms of what it accomplishes, yes, for this kind of "check the same value against several possibilities" pattern. select is often preferred in that specific situation because it can be easier to read, not because it does something if / elseif cannot.

"Do I always need an other branch?" No. other is optional, similar to else in an if block. If none of the when conditions match and there is no other branch, none of the branches run at all.

"Can each when check something completely different, not just the same variable?" Yes. While checking the same variable against different values, as in the customer tier example, is a very common pattern, each when has its own independent condition and does not technically have to compare the same variable.

Quick Recap

• A select block starts with select and ends with endsl, containing one or more when branches and an optional other branch.
• Each when checks its own condition; other covers whatever case is left when no when condition matched.
• Only the first matching branch runs, the same as with if / elseif.
• select is often clearer than a long chain of elseif branches when checking many possible values for essentially the same thing.

Try Asking the AI Tutor

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

• "When should I use select instead of if / elseif?"
• "Can a when condition in RPGLE check more than one value at once?"