$id == $FOO && ($tfoo += $amt) && last SWITCH; depends on the final value of $tfoo being non-zero. If zero, the switct falls through to the default and awards double credit :)
To repair, have 'last' execute unconditionally with the comma operator:
$id == $FOO && ($tfoo += $amt), last SWITCH;

After Compline,
Zaxo

In reply to Re: Pop quiz: find the bug by Zaxo
in thread Pop quiz: find the bug by Ovid

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