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From: jb@cadlab.UUCP (Joerg Battermann)
Newsgroups: comp.lang.pascal
Subject: Re: WANTED: Program for primenumbers
Message-ID: <508@cadlab.cadlab.de>
Date: 27 Jul 89 11:50:22 GMT
References: <1658@eds.ericsson.se>
Reply-To: jb@cadlab.UUCP (Joerg Battermann)
Organization: Cadlab Paderborn, Germany
Lines: 41

In article <1658@eds.ericsson.se> rif_xu@eds.ericsson.se writes:
>
>	Hi,
>	does anybody out there in Netland have a program 
>	(preferably written i C or Pascal) which finds 
>	primenumbers from 1 to a-very-big-number (I have the
>	Sieve of E. but I can't generate those big primes I
>	want on a MacII-maximum up to 50000).
>	
>
>	Thanks Sigge

#include<stdio.h>
#include<math.h>
main()
{
#define  max 1000000                  /* primenumbers <= 1.000.000 */
  register long i,j,k,l;
  long a[max],x,lmax;
  float fmax= max;

  printf("Primenumbers from x to y\n");
  printf("x:");
  scanf("%ld",&x);
  printf("\ny:");
  scanf("%ld",&lmax);
  fmax = lmax;
  k =ceil( sqrt(fmax));

  for(i=2;i<lmax;i++) a[i]=i;

  i=2;
  while( i< k )
  {
    if(a[i] != 0)
	 for(j = 2; (l=i*j)< lmax; j++)
	     a[l] = 0;
    i++;
  }
  for(i=x;i<lmax;i++) if(a[i]!=0) printf("%ld\n",i);
}