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Date: Tue, 1 Apr 2014 23:54:00 +1100
Subject: Re: unicode as valid naming symbols
From: Chris Angelico <rosuav@gmail.com>
Cc: "python-list@python.org" <python-list@python.org>
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On Tue, Apr 1, 2014 at 11:02 PM, Marko Rauhamaa <marko@pacujo.net> wrote:
> ========================================================================
> #include<stdio.h>
>
> int main()
> {
>    int n, i = 3, count, c;
>
>    printf("Enter the number of prime numbers required\n");
>    scanf("%d",&n);
>
>    if ( n >= 1 )
>    {
>       printf("First %d prime numbers are :\n",n);
>       printf("2\n");
>    }
>
>    for ( count = 2 ; count <= n ;  )
>    {
>       for ( c = 2 ; c <= i - 1 ; c++ )
>       {
>          if ( i%c == 0 )
>             break;
>       }
>       if ( c == i )
>       {
>          printf("%d\n",i);
>          count++;
>       }
>       i++;
>    }
>
>    return 0;
> }
> ========================================================================
> (<URL: http://www.programmingsimplified.com/c/source-code/
> c-program-for-prime-number>)

Here's my tweaked version of that:

========================================================================
#include <stdio.h>

int main()
{
   int i = 3, count, factor;

   printf("Enter the number of prime numbers required\n");
   scanf("%d",&count);

   if ( count >= 1 )
   {
      printf("First %d prime numbers are:\n",count);
      printf("2\n");
   }

   while (count > 1)
   {
      /* This is a pretty stupid algorithm */
      for ( factor = 2 ; factor <= i - 1 ; factor++ )
         if ( i%factor == 0 ) break;
      if ( factor == i )
      {
         printf("%d\n",i);
         count--;
      }
      i++;
   }

   return 0;
}
========================================================================

Doesn't change the parenthesis count (other than that I dropped an
unnecessary pair of braces; some people would prefer to keep them, but
I find they're quite superfluous), but improves readability. (Why use
a for loop when you could use a simple while?) As to the question of
whether this is more or less readable than the Scheme version... I
guess that partly depends on the reader's relative familiarity with C
and Scheme, but it's crystal clear to me what the C version is doing -
and that it's doing something stupid. I don't find it more readable to
cast something as recursive; compare these two tight loops:

          (let find-divisor ((c 2))
            (cond
             ((= c i)
              (format #t "~S\n" i)
              (display-primes (1+ count) (1+ i)))
             ((= (remainder i c) 0)
              (display-primes count (1+ i)))
             (else
              (find-divisor (1+ c)))))))))

      for ( factor = 2 ; factor <= i - 1 ; factor++ )
         if ( i%factor == 0 ) break;
      if ( factor == i )
      {
         printf("%d\n",i);
         count--;
      }

In the first one, you start doing something, and if you don't have a
termination point, you recurse - which means you have to name this
loop as a function. In the second, you simply iterate, and then at the
end, decide whether you have the termination condition or not. It's
easy to see what the loop condition is; it's easy to see that it will
always end by one or other termination rule, and then it acts based on
that. Actually, if you switch the conditions, it would look a bit more
like the Scheme version:

      for ( factor = 2 ; i%factor ; factor++ )
      {
        if ( factor == i )
        {
           printf("%d\n",i);
           count--;
           break;
        }
      }

I wouldn't say this makes the code notably more readable, and it
doesn't change the parenthesis count (apart from making more people
want to put the outer braces in - they're still technically optional,
and that was only an optional reduction in the first place), but it's
a closer equivalent and that might make comparison easier.

My view is definitely that the C version is WAY more readable than the
Scheme one.

ChrisA