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Re: Program for testing small numbers

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  • Bigfoot
    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
    Message 1 of 8 , Sep 3, 2004
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      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
      > miltbrown at earthlink.net
      >
      > 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...>
      > > To: <primenumbers@yahoogroups.com>
      > > 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
      > >
      > >
      > >
      > >
    • Hadley, Thomas H (Tom), ALABS
      ... 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 2 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.

        Tom Hadley

        -----Original Message-----
        From: Bigfoot [mailto:plano9@...]
        Sent: Friday, September 03, 2004 5:56 PM
        To: primenumbers@yahoogroups.com
        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
        > miltbrown at earthlink.net
        >
        > 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...>
        > > To: <primenumbers@yahoogroups.com>
        > > 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/


        Yahoo! Groups Links
      • Milton Brown
        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 3 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
          miltbrown at earthlink.net


          > [Original Message]
          > From: Bigfoot <plano9@...>
          > To: <primenumbers@yahoogroups.com>
          > 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
          > > miltbrown at earthlink.net
          > >
          > > 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...>
          > > > To: <primenumbers@yahoogroups.com>
          > > > 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/
          >
          >
          > Yahoo! Groups Links
          >
          >
          >
          >
        • Jim Laird
          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 4 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
            void preload_pl(vector<int> &v)
            {
            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
            preload_pl(base_primes); // initialize the prime
            list

            // sieve numbers between 1001 and 10000
            cout << "Primes between 1001 and 10000\n";
            for (int test = 1001; test < 10000; test += 2) {
            if (test_prime(test, base_primes) == true) {
            cout << test << ", ";
            }
            }

            return;
            }
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