Loading ...
Sorry, an error occurred while loading the content.

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

Expand Messages
  • 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 1 of 8 , Sep 3, 2004
    • 0 Attachment
      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 2 of 8 , Sep 3, 2004
      • 0 Attachment
        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 3 of 8 , Sep 7, 2004
        • 0 Attachment
          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;
          }
        Your message has been successfully submitted and would be delivered to recipients shortly.