Path: chuka.playstation.co.uk!news
From: "JohnT" <johnt@nettech.demon.co.uk>
Newsgroups: scee.yaroze.freetalk.english
Subject: Re: ANSI C code
Date: Tue, 17 Mar 1998 15:54:49 -0000
Organization: PlayStation Net Yaroze (SCEE)
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Message-ID: <6em62v$dud33@chuka.playstation.co.uk>
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Ok, I was only going by what I was taught. Here it is...

The semicolon ; is used to end a statement. Therefore the following are
correct...

for(i=0; i<10; str[i++]=0);
   This uses a null statement because the for loop has no need for a
statement but the ; is still needed or else the next non-looped statement
will be looped.

for(; i<10; i++)....
   This is valid because a for loop HAS to have three argument areas
separated by ;. You could also use this for a continuous loop... for(;;)....
This is because the 'arguments' of a for loop are statements and three are
required for the syntax to be correct (the third is terminated by the close
bracket like an ordinary argument for a function).

The braces { and } are used to enclose a block of statements or a function's
content. So the semicolon ; should not be used. Therefore the following is
incorrect...

for(i=0; i<10; i++)
{
    str[i] = 0;
};

I think that because the K&R specifications don't specifically say this is
illegal it is accepted by most compilers simply because the compiler is
treating the ; as a null statement following the block of code in much the
same way as...

for(i=0; i<10; i++)
{
    str[i] = 0;
} printf("Done\n");


Does this clear things up better?

JohnT

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pal wrote in message <3507E51B.763DB0F2@hotmail.com>...
>> Without having my copy of K&R here, i can't say for sure, but my vote is
for
>> ';' being a legal expression.
>
>The null statement is mentionned in K&R (p18 - on the French version that
is :)).
>They say it's useful for making empty loops, eg :
>for (n = 0 ; getchar() != EOF ; ++n) ; // counts characters
>
>I think it's useful too when your for doesn't need an initializer :
>for (; a==b ;a++) {...}.
>
>Moreover, an "infinite" loop like this one is syntactically correct, too :
>for(;;) {
>    if (...) return ;
>    }
>
>(you may prefer while(1))
>
>And, of course, as Majik pointed out, a macro like the following may lead
to a
>null statement :
>#ifdef DEBUG
>    #define debug(x) printf(x)
>#else
>    #define debug(x)
>#endif
>
>
>> so you should always write macros like:
>>
>> #define DEBUG(x) do { if(debug) printDebug(x) } while(0)
>>
>> the do { } while(0) construct makes the compiler treat the entire block
>> as a single statement, and protects you from the dreaded dangling else.
>> it forces you to use the macro as a function, as well, which is good
>> practice.
>
>Well, what do you think about that :
>
>#define DEBUG(x) { if(debug) printDebug(x) ;}
>
>You can write blocs whereever you can write simple statements. With an
ANSI-C
>compiler, that is... Personnally I often write such blocs in order to
reduce
>variables' visibility (well, I'm not sure this is good English, sorry), and
gcc
>doesn't complain about it (perhaps he knows he'd be deleted from my hd) :
>
>// Note : please be aware that optimisation is not my purpose here :).
>{
>int i ;
>for (something with i) {...}
>}
>
>// later in the same function...
>{
>int i ;
>for (something else with i) {...}
>}
>
>This might not look very useful, but have a look at this one :
>
>f()
>{
>int i ;
>(...lots of code where i isn't used...)
>(last part of code, where i is used, far from its declaration)
>}
>
>Haven't you ever dreamt of writing :
>for (int i = 0 ; i < n ; i++) {...} // Java code
>?
>
>Mmh... I think it's enough, I just needed to talk between two lines of code
+)...
>
>