Erastothenes

[Stewart Gordon]

"davidb" <ta-nospam-zz at gmx.at> wrote in message 
news:f4rvk2$1u7k$1 at digitalmars.com...
> Dave Colling wrote:
>> Has anyone confirmed that the example showing how to find primes
>> by the sieve of Erastothenes actuall works?
>> It certainly counts something, but they are not primes!
>
> You're right, definitely not (includes 0, 1, 4, 8, 10, 14, 20, 22, 25, 
> ...)
> It still features printf instead of writef and is in my opinion
> rather confusing for someone starting to learn by example.
> So here's a cleaned up version, placed in the public domain (hint)

It does work.  You appear to have not seen the line

    prime = i + i + 3;

I added this line

    writefln("i = %d; prime = %d", i, prime);

at the end of the if block to see what's happening.

But there are a few flaws with it.  It sets a bad example not only by using 
printf, but also by being badly commented and by declaring everything in one 
place.  And by using 1 and 0 instead of true and false.

But 3 to 16383 seems a peculiar range to count.  If only it added 1 to the 
count, it would give the number of primes below 1 << 14, which seems more 
what one would expect.

And if multiple iterations are meant to be for benchmarking, 10 is nowhere 
near enough on modern systems.

Stewart.