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From: Keith Thompson <kst-u@mib.org>
Newsgroups: comp.lang.c
Subject: Re: C pointer semantics with dynamically allocated struct
Date: Mon, 17 Aug 2015 12:11:44 -0700
Organization: None to speak of
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Bartc <bc@freeuk.com> writes:
> On 17/08/2015 17:45, Keith Thompson wrote:
>> Bartc <bc@freeuk.com> writes:
>>> On 17/08/2015 02:47, glen herrmannsfeldt wrote:
>> [...]
>>>> I pretty much never write while loops. If I have logic that would
>>>> need one, I write the matching for loop instead.
>>>
>>> That sounds rather perverse. How you thought about whether that makes it
>>> easier or harder for the readers of your code?
>>
>> I agree, but ...
>>
>>> I've just looked at some of my code and I use many hundreds of while
>>> statements, each of which exactly represents what I'm trying to express.
>>> Example:
>>>
>>>    while(a<b) a=a*2;
>>>
>>> I can't really see that it helps matters by writing it as:
>>>
>>>    for (;a<b;a=a*2);
>>
>> Why did you put the "a=a*2" in the header of the for loop?
>
> Why not? It's the sort of thing that would be done by people who like to 
> cram everything into a for-loop.

How did "people who like to cram everything into a for-loop" enter
into the discussion?  It almost seems as if you're trying to make
the for loop as terse and obscure as possible to make some point
about C's for loops.

> What exactly belongs in that third part of a for-loop anyway? 'a' is 
> being tested as the exit condition, and it is a that is being updated to 
> its next value.

It's hard to see the intent without more context, but the behavior of
the original while loop:

    while(a<b) a=a*2;

is to double a zero or more times until it equals or exceeds the
value of b.  For example, it might be used to compute the smallest
power of two whose value is at least that of b (if the initial
value of a is 1).  The value of a would then be used after the end
of the loop (unlike a typical
    for (i = 0; i < N; i ++)
loop where the value of i is usually used only within the loop).

If that's the intent, then IMHO the while loop is the clearest way to
write it in C (though I'd write `a *= 2;` rather than `a=a*2;`), and
the equivalent for loop is most clearly written with the same body.

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Working, but not speaking, for JetHead Development, Inc.
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"