## RE: [PrimeNumbers] Re: Program for testing small numbers

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• ... First of all, he wrote k != 0 , not k !== 0 and the first is basic C/C++ code. There is no confusion with the factorial. ... No, it s the remainder
Message 1 of 8 , Sep 3, 2004
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Bigfoot wrote:

>> k!==0 //pointless, no need to do factorial here

First of all, he wrote "k != 0", not "k !== 0" and the first is
basic C/C++ code. There is no confusion with the factorial.

>>i%50 //wouldn't that be if the remainder is 50?

No, it's the remainder after dividing by 50.

Please read a book on intro to C or C++ before questioning someone's program. It looks to me like Milton's program is a valid, if inefficient, prime number generator.

-----Original Message-----
From: Bigfoot [mailto:plano9@...]
Sent: Friday, September 03, 2004 5:56 PM
Subject: [PrimeNumbers] Re: Program for testing small numbers

I'm working on turning that into c++ code that I can use, but I don't
see what the purpose of the lines
k!==0 //pointless, no need to do factorial here

and
i%50 //wouldn't that be if the remainder is 50?

--- In primenumbers@yahoogroups.com, "Milton Brown" <miltbrown@e...>
wrote:
> A program in Java (C++) for small primes is attached.
>
> Milton L. Brown
>
> public class Prime
> {
> public static void main(String[] args)
> {
>
> int i, j, k;
> for (i = 2; i<3000; i++)
> { k = 1;
> for ( j=2; j<i; j++) {
> k = i %j;
> if (k == 0) break;
> }
> if ((i% 50)==0) System.out.println(" ");
> if (k !=0) System.out.print(i+" ");
>
> };
>
> }
> }
>
>
> > [Original Message]
> > From: Bigfoot <plano9@y...>
> > Date: 9/2/2004 5:48:35 PM
> > Subject: [PrimeNumbers] Re: Program for testing small numbers
> >
> > I did a quick scan of the files and didn't see a sieve for
finding
> > small primes. I may have missed one if it was there, can someone
> > give me a link to one (written in c or c++)
> >
> >
> >
> >
> > Unsubscribe by an email to: primenumbers-
unsubscribe@yahoogroups.com
> > The Prime Pages : http://www.primepages.org/
> >
> >
> >
> >
> >
> >

Unsubscribe by an email to: primenumbers-unsubscribe@yahoogroups.com
The Prime Pages : http://www.primepages.org/

• For the small prime lister program, the outer for-loop is exited as soon as i is found to be composite. The number is not composite (prime) when k != 0,
Message 2 of 8 , Sep 3, 2004
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For the small prime lister program, the outer for-loop
is exited as soon as i is found to be composite. The
number is not composite (prime) when k != 0, otherwise it
is composite. This line is required to print the primes.

The line with (i % 50) = = 0 will print a line-return, with less
than 50 primes on a single line of out-put, so that many primes
can be seen on a single page.

Milton L. Brown

> [Original Message]
> From: Bigfoot <plano9@...>
> Date: 9/3/2004 3:56:43 PM
> Subject: [PrimeNumbers] Re: Program for testing small numbers
>
> I'm working on turning that into c++ code that I can use, but I don't
> see what the purpose of the lines
> k!==0 //pointless, no need to do factorial here
> and
> i%50 //wouldn't that be if the remainder is 50?
>
> --- In primenumbers@yahoogroups.com, "Milton Brown" <miltbrown@e...>
> wrote:
> > A program in Java (C++) for small primes is attached.
> >
> > Milton L. Brown
> >
> > public class Prime
> > {
> > public static void main(String[] args)
> > {
> >
> > int i, j, k;
> > for (i = 2; i<3000; i++)
> > { k = 1;
> > for ( j=2; j<i; j++) {
> > k = i %j;
> > if (k == 0) break;
> > }
> > if ((i% 50)==0) System.out.println(" ");
> > if (k !=0) System.out.print(i+" ");
> >
> > };
> >
> > }
> > }
> >
> >
> > > [Original Message]
> > > From: Bigfoot <plano9@y...>
> > > Date: 9/2/2004 5:48:35 PM
> > > Subject: [PrimeNumbers] Re: Program for testing small numbers
> > >
> > > I did a quick scan of the files and didn't see a sieve for
> finding
> > > small primes. I may have missed one if it was there, can someone
> > > give me a link to one (written in c or c++)
> > >
> > >
> > >
> > >
> > > Unsubscribe by an email to: primenumbers-
> unsubscribe@yahoogroups.com
> > > The Prime Pages : http://www.primepages.org/
> > >
> > >
> > > Yahoo! Groups Links
> > >
> > >
> > >
> > >
>
>
>
>
> Unsubscribe by an email to: primenumbers-unsubscribe@yahoogroups.com
> The Prime Pages : http://www.primepages.org/
>
>
>
>
>
>
• Here s a simple, simple prime number tester for very small numbers. It saves the previous results of test searches in memory, so it will be impractical if you
Message 3 of 8 , Sep 7, 2004
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Here's a simple, simple prime number tester for very small numbers. It
saves the previous results of test searches in memory, so it will be
impractical if you search for primes that are too large (depending on
how much memory is on your system). It also uses STL classes for
containers etc. Worked on my system. Change main() as required. Only
checks up to the square root of the test number as a slight
optimization.

Cheers, Jim

========================================================================
=====

#include <string>
#include <vector>
#include <ostream>

using namespace std;

// loads the prime list with the initial primes
{
v.resize(6);
v[0]=2; v[1]=3; v[2]=5;
v[3]=7; v[4]=11; v[5]=13;
return;
}

// returns true if testnum is prime. Adds primes to v as necessary
bool test_prime(int testnum, vector<int> &v)
{
// check the first few primes
for (unsigned int i = 0; i < 5; i++)
if (testnum % v[i] == 0) return false;

// check the rest of the list
for (unsigned int i = 5; i < v.size(); i++) {
if (testnum % v[i] == 0) return false;
if (testnum < (v[i]*v[i])) return true;
}

// at the end of the prime list, increase it till you hit the
test
// or determine that testnum is composite

for(int x = v[v.size()-1] + 2; ; x += 2) {
if (test_prime(x, v) == true) {
v.push_back(x);
if (testnum % x == 0) return false;
if ((x*x) > testnum) return true;
}
}
}

void main(int argv, char **argc)
{
vector<int> base_primes;

// initialize vector
base_primes.reserve(1000); // make room for 1000
entries to begin with