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From: mfinney@lynchburg.net
Subject: Re: Software landmines (loops)
Date: 1998/09/17
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In <gio+van+no+ni+8-1609981736190001@dialup47.tlh.talstar.com>, gio+van+no+ni+8@tal+star+spam.com (Giovanni 8) writes:
>> Michael Lee Finney wrote:
>> I have made a study of many control structures for years
>> as a hobby and virtually all of them are tree-structured,
>> but they are not structured.
>
>Virtually all of them are tree-structured but not structured?
>
>Virtually all of them are 4-wheeled vehicles but not wheeled
>vehicles?
>
>Since tree-structures are a sub-set of all possible structures,
>then they must be structures.

You misunderstand.  You are applying general analogy to the
situation, but it is invalid because these terms have specific
technical meanings.

Code which is structured only allows a single entry, single exit
with some possible argument as to exactly which control structures
are valid.  Traditionalists will argue, for example, that a mid-loop
exit is not acceptable and others will disagree.

Code which is tree-structured essentially allows any control
structure which does not contain a jump into the middle of a
block.  Or, another way of expressing the concept, you may
exit or repeat any block any number of times at any depth of
block nesting.  Neither structured code nor tree-structured code
allows unrestricted use of the GOTO statement.  Under these
definitions, all structured code is tree-structured, but not vice-
versa.


Michael Lee Finney