Eratosthenes.c

#include<stdio.h>

  typedef enum bool {false, true} boolean ;

/*  Input: an integer n > 1
 *
 *  Let A be an array of Boolean values, indexed by integers 2 to n,
 *  initially all set to true.
 *
 *  for i = 2, 3, 4, ..., while i ≤ n/2:
 *    if A[i] is true:
 *      for j = 2i, 3i, 4i, ..., while j ≤ n:
 *        A[j] = false
 *
 *  Now all i such that A[i] is true are prime.
 *
 */

int main(void)
{


  int i , j, intmax ;

  printf("Enter limit > ") ;
  scanf("%d", &intmax) ;

  int A[intmax] ;                /*Array of integers to be Sieved*/

  for( i=0 ; i<=intmax ; i++ )   /*Populate the array with consecutive integers*/
  {
    A[i] = true ;
  }

  for( i=2 ; i <= intmax ; i++)
  {
    if(A[i] == true)
    {
      printf("%d\n", i) ;
      for( j=2 ; j*i<=intmax ; j++)
      {
        A[i*j] = false ;
      }
    }
  }

return 0 ;
}