tk5-c90-projects/src/SIEVE01.c

#include<stdio.h>

#define LIMIT 10000
#define PRIMES 1000

// Sieve of Eratosthenes
// Author: Greg Gauthier
int main()
{
   int i,j,numbers[LIMIT];
   int primes[PRIMES];

   for (i=0;i<LIMIT;i++)
   {
      numbers[i]=i+2;
   }

   for (i=0;i<LIMIT;i++)
   {
      if (numbers[i]!=-1)
      {
         for (j=2*numbers[i]-2;j<LIMIT;j+=numbers[i])
            numbers[j]=-1;
      }
   }

   j = 0;
   for (i=0;i<LIMIT&&j<PRIMES;i++)
     if (numbers[i]!=-1)
        primes[j++] = numbers[i];

   printf("\n");
   printf("PRIME NUMBERS BETWEEN 1 AND %d\n",LIMIT);
   printf("TOTAL PRIMES FOUND: %d\n\n",PRIMES);
   printf("LIST OF PRIMES:\n\n");

   for (i=0;i<PRIMES;i++)
      if (i % 20 == 0)
      {
         printf("\n %4d ",primes[i]);
      }
      else
      {
         printf("%4d  ",primes[i]);
      }

   return 0;
}