IF, DO, and Basic Control Flow in CLLE

Learning Objective

By the end of this lesson, you will be able to read and write a simple IF / THEN / ELSE structure in CLLE, including a DO / ENDDO group for more than one command, using CL's comparison operators.

Simple Explanation

In the Variables in CLLE lesson, every example ran straight through from top to bottom. CL's IF command lets a CLLE program's behavior depend on a condition, similar in purpose to if in RPGLE, though with CL's own keyword-based syntax.

A simple IF command looks like this:

DCL VAR(&ORDERTOTAL) TYPE(*DEC) LEN(9 2)
DCL VAR(&MSG) TYPE(*CHAR) LEN(50)

CHGVAR VAR(&ORDERTOTAL) VALUE(150.00)

IF COND(&ORDERTOTAL *GT 100) THEN(CHGVAR VAR(&MSG) VALUE('Large order'))

Here, COND holds the condition being checked, using CL's comparison operators, such as *GT (greater than), *LT (less than), *EQ (equal to), and *NE (not equal to). THEN holds the single command to run if the condition is true.

When more than one command needs to run for a condition, THEN is paired with DO, starting a group of commands that ends with ENDDO:

IF COND(&ORDERTOTAL *GT 100) THEN(DO)
  CHGVAR VAR(&MSG) VALUE('Large order')
  SNDPGMMSG MSG(&MSG)
ENDDO
ELSE CMD(CHGVAR VAR(&MSG) VALUE('Normal order'))

ELSE provides a command, or a DO group, to run when the condition was false. ELSE is optional; an IF with only a THEN is a complete, valid structure on its own.

Why It Matters

Conditional logic in CLLE lets a program make decisions, such as choosing a different message, a different program to call, or a different next step, based on the data or situation it encounters, the same fundamental role conditional logic plays in RPGLE. Recognizing IF / THEN / ELSE, and knowing when a DO group is needed, is essential to reading or writing any CLLE program more complex than a fixed sequence of commands.

Practical Example

Imagine a CLLE program deciding how to handle an order based on its total. For an order total of 150.00, the condition &ORDERTOTAL *GT 100 is true, so the DO group's commands run: setting &MSG to 'Large order' and sending that message. If the order total had instead been 50.00, the condition would be false, and the ELSE command would run instead, setting &MSG to 'Normal order'.

This is a simplified, illustrative example rather than a specific real order-handling policy, but it reflects a very common, everyday use of conditional logic in CLLE.

Common Confusions

"Do I always need DO and ENDDO with IF?" No. DO and ENDDO are only needed when more than one command should run for a condition. A single command can be given directly to THEN, as shown in the first example, without a DO group at all.

*"Are CL's comparison operators like GT the same as RPGLE's > and >= operators?" They serve the same purpose, comparing two values, but CL uses its own keyword-style operators, such as *GT, *LT, *EQ, and *NE, rather than the symbolic operators used in RPGLE expressions.

"Can I nest an IF inside a DO group?" Yes. A DO group can contain another IF command among its statements, similar to nesting conditional logic in RPGLE, letting a program check additional conditions within a branch that already matched an outer condition.

Quick Recap

• IF COND(...) THEN(...) runs a single command when a condition is true; ELSE CMD(...) runs a command when it is false, and is optional.
• DO and ENDDO group more than one command together under THEN or ELSE.
• CL uses keyword-style comparison operators, such as *GT, *LT, *EQ, and *NE, in place of RPGLE's symbolic operators.
• Conditional logic lets a CLLE program's behavior depend on the data or situation it encounters, just as it does in RPGLE.

Try Asking the AI Tutor

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

• "What are some other CL comparison operators besides *GT, *LT, *EQ, and *NE?"
• "Can ELSE be followed by its own DO group instead of a single command?"