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Groups > comp.lang.c > #150307
| From | Ben Bacarisse <ben.usenet@bsb.me.uk> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: After doing a lot of the problems on codingbat.com |
| Date | 2020-02-27 20:42 +0000 |
| Organization | A noiseless patient Spider |
| Message-ID | <87mu93vk1j.fsf@bsb.me.uk> (permalink) |
| References | <2f146b5c-e025-46ef-af7b-7c328c9f4206@googlegroups.com> <20200227200243.157a5e51fe7577f22aa37378@g{oogle}mail.com> <r396mg$uob$1@dont-email.me> |
Lew Pitcher <lew.pitcher@digitalfreehold.ca> writes:
> Anton Shepelev wrote:
>
>> chad:
>>
>>> I've come to this horrible realization that I don't
>>> understand a for loop as well as what I thought I did.
>>
>> Just don't abuse the for loop, cramping all kinds of
>> unrelated code into its control expressions. Always use\
>> it as a loop with a counter:
> [snip]
>
> Good advice to someone who doesn't understand how to use a for() loop.
>
> However, once chad gets past the basic understanding, there's a lot more you
> can do with for() than just count loops
>
> You can
> - find the end of a string
> char *ptr;
> for (ptr = "string" ; *ptr ; ++ptr) continue;
char *ptr = strchr("string", 0);
> - or count the number of characters
> char *ptr;
> size_t nchars;
> for (ptr = "string", nchars = 0 ; *ptr ; ++ptr) ++nchars;
size_t nchars = strlen("string");
Obviously you know about these function, but it's way better to give
examples that aren't re-inventing the wheel. Pointer scanning is a
common use of a 'for' loop but I'd choose a task that isn't a library
function:
size_t count = 0;
for (const char *ptr = str; *ptr; ptr++)
if (*ptr == ' ')
count += 1;
> - or traverse a linked list
> struct list { struct list *next; int valu; } *root = NULL;
> /* ... */
> for (struct list *node = root; node; node = node->next)
> {
> /* do something with this node */
> }
>
> - or even perform a binary search through an ordered array
> int *binsearch(int key, int array[], size_t nelement)
> {
> size_t lowpt = 0, /* lowest index in search range */
> midpt, /* midpoint index; where to search */
> highpt = nelement - 1; /* highest index in search range */
This function can't search and empty array. For that reason, I prefer
to keep the search in a half-open interval [low, high).
> /* LOOP through search UNTIL match found OR no elements left to search */
> for (midpt = (lowpt+highpt)/2; /* start in the middle */
> array[midpt] != key && highpt > lowpt; /* not found AND in bounds*/
> midpt = (lowpt+highpt)/2) /* compute new midpoint */
> { /* ============================ **
> ** array[midpt] was NOT a match **
> ** ============================ */
> if (key > array[midpt])
> lowpt = midpt + 1; /* narrow search to between here and high */
> else
> highpt = midpt - 1; /* narrow search to beween low and here */
> }
>
> /* loop terminates when entry found OR no more array to search */
>
> return (array[midpt] == key ? array+midpt : NULL);
> }
For me, this is a step too far. The double midpt calculation and test
for both array[midpt] != key and array[midpt] == key would make me
investigate alternatives. I think I've always ended up using a while
loop for this sort of search.
> A good programmer doesn't limit themselves to using for() strictly as a
> counted loop.
Ack.
--
Ben.
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After doing a lot of the problems on codingbat.com chad <cdalten@gmail.com> - 2020-02-25 06:55 -0800
Re: After doing a lot of the problems on codingbat.com Anton Shepelev <anton.txt@g{oogle}mail.com> - 2020-02-27 20:02 +0300
Re: After doing a lot of the problems on codingbat.com James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-02-27 11:41 -0800
Re: After doing a lot of the problems on codingbat.com Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2020-02-27 14:48 -0700
Re: After doing a lot of the problems on codingbat.com Bart <bc@freeuk.com> - 2020-02-27 23:17 +0000
Re: After doing a lot of the problems on codingbat.com James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-02-27 16:40 -0800
Re: After doing a lot of the problems on codingbat.com Bart <bc@freeuk.com> - 2020-02-28 01:08 +0000
Re: After doing a lot of the problems on codingbat.com Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-02-28 01:37 -0800
Re: After doing a lot of the problems on codingbat.com James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-02-28 06:21 -0800
Re: After doing a lot of the problems on codingbat.com Bart <bc@freeuk.com> - 2020-02-28 16:15 +0000
Re: After doing a lot of the problems on codingbat.com James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-02-28 10:37 -0800
Re: After doing a lot of the problems on codingbat.com Bart <bc@freeuk.com> - 2020-02-28 19:22 +0000
Re: After doing a lot of the problems on codingbat.com David Brown <david.brown@hesbynett.no> - 2020-03-01 14:54 +0100
Re: After doing a lot of the problems on codingbat.com Bart <bc@freeuk.com> - 2020-03-01 15:36 +0000
Re: After doing a lot of the problems on codingbat.com David Brown <david.brown@hesbynett.no> - 2020-03-01 17:08 +0100
Re: After doing a lot of the problems on codingbat.com Richard Damon <Richard@Damon-Family.org> - 2020-02-27 21:57 -0500
Really??? (Was: After doing a lot of the problems on codingbat.com) gazelle@shell.xmission.com (Kenny McCormack) - 2020-02-28 13:06 +0000
Re: Really??? (Was: After doing a lot of the problems on codingbat.com) chad <cdalten@gmail.com> - 2020-02-28 05:47 -0800
Re: Really??? (Was: After doing a lot of the problems on codingbat.com) James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-02-28 05:59 -0800
Re: After doing a lot of the problems on codingbat.com Bart <bc@freeuk.com> - 2020-02-28 14:04 +0000
Re: After doing a lot of the problems on codingbat.com Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-02-28 17:50 +0000
Re: After doing a lot of the problems on codingbat.com Anton Shepelev <anton.txt@g{oogle}mail.com> - 2020-02-28 20:59 +0300
Re: After doing a lot of the problems on codingbat.com Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-02-28 22:37 +0000
Re: After doing a lot of the problems on codingbat.com Bart <bc@freeuk.com> - 2020-02-29 00:17 +0000
Re: After doing a lot of the problems on codingbat.com Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-02-29 01:01 +0000
Re: After doing a lot of the problems on codingbat.com Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-04-02 19:22 -0700
Re: After doing a lot of the problems on codingbat.com Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2020-02-27 14:52 -0500
Re: After doing a lot of the problems on codingbat.com Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-02-27 20:42 +0000
Re: After doing a lot of the problems on codingbat.com David Brown <david.brown@hesbynett.no> - 2020-02-27 22:59 +0100
Re: After doing a lot of the problems on codingbat.com Bart <bc@freeuk.com> - 2020-02-27 20:48 +0000
Re: After doing a lot of the problems on codingbat.com Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-03-27 20:06 -0700
Re: After doing a lot of the problems on codingbat.com chad <cdalten@gmail.com> - 2020-02-27 15:28 -0800
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