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From: Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups: comp.lang.c
Subject: Re: for() syntax (Was: Christmas Quiz 2022)
Date: Mon, 26 Dec 2022 06:48:57 -0800
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Lew Pitcher <lew.pitcher@digitalfreehold.ca> writes:

> [...concerning the syntax of for() statements...]
>
> Consider (from N1570)
>
>   6.7 Declarations
>     Syntax
>       declaration:
>         declaration-specifiers init-declarator-list[opt] ;
>         static_assert-declaration
>
>       declaration-specifiers:
>         storage-class-specifier declaration-specifiers[opt]
>         type-specifier declaration-specifiers[opt]
>         type-qualifier declaration-specifiers[opt]
>         function-specifier declaration-specifiers[opt]
>         alignment-specifier declaration-specifiers[opt]
>
>       init-declarator-list:
>         init-declarator
>         init-declarator-list , init-declarator
>
>       init-declarator:
>         declarator
>         declarator = initializer
>
> And
>   6.8.5 Iteration statements
>     Syntax
>       iteration-statement:
>         while ( expression ) statement
>         do statement while ( expression ) ;
>         for ( expression[opt] ; expression[opt] ; expression[opt] ) statement
>         for ( declaration expression[opt] ; expression[opt] ) statement
>
> (The square brackets here denotes a subscript)
>
> Does not the second form of the for() statement
>     for ( declaration expression[opt] ; expression[opt] ) statement
> permit the declaration part to /not/ have an initializer?  As in
>     for ( int i; i>0; ++i) continue;

Yes, it does, and clearly that is deliberate.

> While it looks "legal" to me, it certainly seems suspect.  I would
> have expected the standard to /require/ that the "declaration" part
> of the for() statement include an initializer.

Consider the following for() statement, which is allowed by the C
standard:

    for(  int i = 0, j, k;  i < N;  i++  )  ...

Would you insist that 'j' and 'k' also have initializers?

It seems obvious that the syntax for for() statements simply
reused the syntax for _declaration_ so as not to complicate the
language.  Whether declaring a non-initialized variable is useful
or not (and there are cases where it can be useful), that is not
sufficiently important to complicate the language by adding more
syntax (or a constraint).

Remember Flon's Law:  there has never been, nor will there ever
be, a programming language in which it is the least bit difficult
to write bad programs.

What I think is funnier is that the for() statement below is also
allowed (as of C11):

    for(
        _Static_assert( 1 > 0, "fooled you!" );
        c = getchar(),  c != EOF;
        /* nothing */
    ){
        ...
    }

Here again, the negative consequence of allowing a _Static_assert
in a for() statement is outweighed by the cost of expanding the
syntax.  Special cases are anathema to ease of remembering and
ease of understanding.  Natural languages with lots of irregular
verbs are harder to learn than those with few irregular verbs.
The same idea applies to programming languages.