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From: Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups: comp.lang.c
Subject: Re: How to avoid an overflow during multiplication?
Date: Sun, 15 May 2022 07:19:01 -0700
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dave_thompson_2@comcast.net writes:

> (Sorry for delay, I just found this somehow went in a file folder
> instead of outbox)
>
> On Fri, 04 Feb 2022 21:14:59 -0800, Tim Rentsch
> <tr.17687@z991.linuxsc.com> wrote:
>
>> Mateusz Viste <mateusz@xyz.invalid> writes:
>>
>>> so let me ask:  what C99 feature do you use, that you wouldn't want
>>> to loose?
>
> ...
>
>> First there are several constructs that C89/C90 permits but are
>> disallowed in C99:
>
> ...
>
>>   * 'return' statements need not give an expression in a
>>     function that returns a non-void type, and conversely
>>
>> I understand why K&R C (and later C89/C90) allowed these things.
>
> ...
> Not conversely.  return expr in void function was a constraint
> violation in C89/90.  (And impossible in K&R which had no void.)

Thank you for the follow-up (and no worries about the delay).

To the best of my knowledge all of the following are true
statements.

K&R C did not have a void type (although some pre-standard C
compilers may have had support for void).

In both the ANSI C standard (C89) and the first ISO C standard
(C90), a return statement with an expression is a constraint
violation if it appears in a function whose return type is void
(although some pre-standard C compilers may not have observed
this rule).

K&R C, C89, and C90 all allow things like this:

    int
    f(){
        ...
        return;
    }

    g(){
        ...
        return  0;
    }

In the ISO C99 standard, paragraph 5 in the Foreword says (in
part) the following:

    This second edition cancels and replaces the first edition,
    ISO/IEC 9899:1990, as amended and corrected by ISO/IEC
    9899/COR1:1994, ISO/IEC 9899/AMD1:1995, and ISO/IEC
    9899/COR2:1996.  Major changes from the previous edition
    include:

        [...]

        -- return without expression not permitted in function
           that returns a value (and vice versa)

I hope these observations clarify my earlier comment.