Date: Tue, 23 Oct 2007 23:32:53 +0100 From: Bruce Cran <bruce@cran.org.uk> To: Derek Ragona <derek@computinginnovations.com> Cc: freebsd-questions@freebsd.org, Harald Schmalzbauer <h.schmalzbauer@omnisec.de> Subject: Re: Mentor for C self study wanted Message-ID: <471E7695.1050702@cran.org.uk> In-Reply-To: <6.0.0.22.2.20071023171535.0244b420@mail.computinginnovations.com> References: <200710232044.53240.h.schmalzbauer@omnisec.de> <20071023220134.3abd635e@epia-2.farid-hajji.net> <20071023162454.93851854.wmoran@potentialtech.com> <200710232324.09851.h.schmalzbauer@omnisec.de> <6.0.0.22.2.20071023171535.0244b420@mail.computinginnovations.com>
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Derek Ragona wrote:
> At 04:24 PM 10/23/2007, Harald Schmalzbauer wrote:
>> Am Dienstag, 23. Oktober 2007 22:24:54 schrieb Bill Moran:
>> > In response to cpghost <cpghost@cordula.ws>:
>> > > On Tue, 23 Oct 2007 20:44:52 +0200
>> > >
>> > > Harald Schmalzbauer <h.schmalzbauer@omnisec.de> wrote:
>> > > > The first one was for example the attached code: Why does it
>> segfault?
>> > >
>> > > Mailman ate the attachment... Can't see it here.
>> >
>> > I may be out of line, but I think if you're using FreeBSD as your
>> > learning platform, that it wouldn't be a problem to ask this list.
>> >> Harald Schmalzbauer wrote:
>> > > Am Dienstag, 23. Oktober 2007 21:43:52 schrieben Sie:
>> > >>> Hello Aryeh,
>> > >>>
>> > >>> I'm willing to pay fair fees, but are you interested in "micro
>> payment"
>> > >>> ;) ?
>> > >>
>> > >> For other reasons I love micro payments.
>> > >>
>> > >>> Serious, I'll have the one or other short question per week (I'm
>> > >>> usually busy, just making spare time lessons from my book (UTC-1
>> spare
>> > >>> time)).
>> > >>
>> > >> Just so I know what level to present on what is your background
>> in CS
>> > >> and programming?
>> > >
>> > > CS??
>> > > I'm able to solve problems analytically, but I don't know any
>> language
>> > > really well.
>> > > I know bourne shell, csh, pascal, and basic. And a tiny bit asm, but
>> > > that's been on ZX81.
>> >
>> > Although, you'll have to include your code inline to get past the
>> > sanitizers.
>>
>> Thanks all,
>>
>> here was my example, just for completeness, I found mentors for my needs.
>>
>> Thanks a lot to all!
>>
>>
>> #include <stdio.h>
>>
>> void main()
>> {
>> short nnote;
>>
>> // Numerischen Notenwert einlesen
>> printf("Bitte numerischen Schulnotenwert eingeben: ");
>> scanf("%d",&nnote);
>>
>> switch (nnote)
>> {
>> case 1: printf("Die Note %d entspricht sehr gut.",nnote);
>> break;
>> case 2: printf("Die Note %d entspricht gut.",nnote);
>> break;
>> case 3: printf("Die Note %d entspricht befriedigend.",nnote);
>> break;
>> case 4: printf("Die Note %d entspricht ausreichend.",nnote);
>> break;
>> case 5: printf("Die Note %d entspricht mangelhaft.",nnote);
>> break;
>> case 6: printf("Die Note %d entspricht ungenügend.",nnote);
>> break;
>> default: printf("%d ist keine zulässige Schulnote!");
>> }
>> printf("\n");
>> }
>>
>> P.S.:
>> I found that declaring nnote as int soleves my problem, but I couldnÄt
>> understand why.
>> Another one was the result of default: nnote was -1077942208 instead
>> of 9 for
>> example.
>
> if you check the man page on scanf:
> d Matches an optionally signed decimal integer; the next pointer must
> be a pointer to int.
>
> You shouldn't try to put a short into an int. Always declare the
> correct size for variables. Your segv is because scanf was trying to
> put an int where it won't fit.
>
> You will get the same result if you go off the end of an array.
>
> -Derek
>
It's well worth increasing the number of warnings enabled when writing C
code, to catch any errors early on. -Wall catches this sort of mistake.
Compiling your code gives the following output:
> gcc -Wall test.c -o test
test.c:4: warning: return type of 'main' is not 'int'
test.c: In function 'main':
test.c:9: warning: format '%d' expects type 'int *', but argument 2 has
type 'short int *'
--
Bruce Cran
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