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From: Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups: comp.lang.c
Subject: Re: Comma operator in for() statements
Date: Fri, 27 Mar 2020 06:46:06 -0700
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luser droog <luser.droog@gmail.com> writes:

> [how to make for() variables be const]
>
> I've tried to shake the habit of seeing macros everywhere,
> but this is getting to the length where a macro might be an
> appropriate way to use this idiom.
>
> #define FOR_UP(IDX, INI, LIM, BODY)  \
>   for(  int IDX ## __LINE__ = (INI); \
>         IDX ## __LINE__ < (LIM);     \
>         ++ IDX ## __LINE__  ){       \
>     int const IDX = IDX ## __LINE__; \
>     BODY;                            \
>   }

Maybe so but this macro isn't it.

  (1) Type of iteration variable should be a parameter,
      not fixed.

  (2) The usage '## __LINE__' doesn't work.

  (3) The "test" and "increment" should both be more
      general.

  (4) Perhaps most important, the loop body should
      not be a parameter.  Ick and double ick.

Challenge:  write a macro definition that addresses each
of the above concerns.  Specifically with regard to point
(4), the macro expansion should act like a 'for(...)'
prefix, so the loop body statement comes after the macro
call, eg,

    P_FOR( int, i, 0, < 10, ++ ){
        sum += a[i];
    }

(Yes there are hints there for some of the other points.)