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From: Dan Purgert <dan@djph.net>
Newsgroups: comp.lang.c
Subject: Re: else ladders practice
Date: Thu, 31 Oct 2024 14:34:46 -0000 (UTC)
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On 2024-10-31, fir wrote:
> Dan Purgert wrote:
>> On 2024-10-31, fir wrote:
>>> somethins i got such pices of code like
>>>
>>> if(n==1) {/*something/}
>>> if(n==2) {/*something/}
>>> if(n==3) {/*something/}
>>> if(n==4) {/*something/}
>>> if(n==5) {/*something/}
>>>
>>> technically i would need to add elses - but the question is if to do that
>>>
>>> do teh code has really chance to be slower without else (except some
>>> very prmitive compilers) ??
>>
>> In the above, all conditionals are always checked -- that is the truth
>> of a previous conditional statement has no bearing on subsequent tests.
>> This leads to the potential of tests going off in directions you hadn't
>> necessarily anticipated.
>>
>> However, 'if..elseif..else' will only check subsequent conditionals if
>> the prior statements were false.  So for the case that "n=2", you're
>> only ever testing the two cases "if (n==1)" (which is false) and
>> "elseif(n==2)".  The computer just skips to the end of the set of
>> statements.
>>
>>
>> Given this MWE (my own terrible code aside ;) ):
>>
>>    int main(){
>>      int n=0;
>>      printf ("all if, n=%u\n",n);
>>      if (n==0) { printf ("n: %u\n",n); n++;}
>>      if (n==1) { printf ("n: %u\n",n); n++;}
>>      if (n==2) { printf ("n: %u\n",n); n++;}
>>      if (n==3) { printf ("n: %u\n",n); n++;}
>>      if (n==4) { printf ("n: %u\n",n); n++;}
>>      printf ("all if completed, n=%u\n",n);
>>
>>      n=3;
>>      printf ("with else if, n=%u\n",n);
>>      if (n==0) { printf ("n: %u\n",n); n++;}
>>      else if (n==1) { printf ("n: %u\n",n); n++;}
>>      else if (n==2) { printf ("n: %u\n",n); n++;}
>>      else if (n==3) { printf ("n: %u\n",n); n++;}
>>      else { printf ("n: %u\n",n); n++;}
>>      printf ("with else if completed, n=%u\n",n);
>>    }
>>
>>
>> You'll get the output:
>>
>> all if, n=0
>> n: 0
>> n: 1
>> n: 2
>> n: 3
>> n: 4
>> all if completed, n=5
>> with else if, n=3
>> n: 3
>> with else if completed, n=4
>>
>> HTH :)
>>
> i not modify n in those {} blocks so this example is not much relevant

I'm using that as a simplified case to force the issue.  "n" could be
modified anywhere, just so long as it is "between" any two of the test
cases being checked.

>
> my quiestion is more liek what is a metter of beter style

If it is a series of related conditions, then "if .. else if .. else".

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