FOR_LOOP_VAR_MODIFIED

Severity: warn. PLCopen: L12 — a FOR loop counter shall not be modified inside the loop body.

The loop counter is assigned to inside the loop body. Per IEC 61131-3 and PLCopen, doing this is undefined — implementations may honour the new value, ignore it, or loop unexpectedly long. Either way the loop's intent is gone.

Settings. No check-specific config.

Trigger.

FOR i := 1 TO 10 DO
    i := i + 2;                       (* fires — skips iterations *)
END_FOR;

The bot posts.

🟧 warn  FOR_LOOP_VAR_MODIFIED
FOR-loop counter 'i' assigned inside the loop body (PLCopen L12)

Fix. Use a WHILE loop if the iteration count is genuinely dynamic. If you just wanted a different step, use the BY clause of the FOR (FOR i := 1 TO 10 BY 2 DO).