/******************
** sample array program
**
** the Sieve of Erostothenese 
** this progam finds and prints all the prime numbers
** between 2 and 100 (MAX)
**
** the indexes into the arrary represent the integers
**
** DL FREY
** 11/20/98
**
*********************************/
#include <stdio.h>

#define MAX 1000
#define TRUE 1
#define FALSE 0

main ()
{
   /* declare an array that contains MAX integers */
   int primes[MAX];

   int i, j, columns;

   /* initialize each element of the array to TRUE */
   for (i = 0; i < MAX;  i++)
   {
	primes[i] = TRUE;
   }

   /* 0 and 1 are NOT primes, by definition, so
   ** make them FALSE
   */ 
   primes[0] = primes[1] = FALSE;

   /* for each integer.... */
   for (i = 2; i < MAX; i++)
   {
      /* check all the integers that are larger
      ** any integer, j,  that is a multiple of i
      ** is NOT prime
      */
      for (j = i + 1; j < MAX; j++)
      {
	  /* this statement checks if j is evenly divisible by i
          ** i.e. the remainder is 0... if so j is NOT prime
          */
	  if ((j % i) == 0)
	  {
	    primes[j] = FALSE;
	  }
      }
   }

   /* now print all the primes 
   ** in neat columns, 10 per row
   */
   columns = 1;
   for (i = 0; i < MAX; i++)
   {
      if (primes[i] == TRUE)
      {
	/* using %6d gives us columns that are neatly aligned */
	printf ("%6d", i);

	/* see if we have printed 10 columns
	** is so, print a newline and go to the next row
	** and start counting columns over again
	*/
	if (++columns > 10)
	{
	    printf ("\n");
	    columns = 1;
	}
      }
   }

   /* print a newline at the end
   ** for the last row
   */
   printf ("\n");
}