指针之6.4

/*
 * 用埃拉托色尼(Eratosthense)算法计算质数.
 * Sieve of Dratosthense -- compute prime numbers using an array
 * 2010-11-20
 */

#include <stdlib.h>

#define SIZE    1000

#define TRUE    1
#define FALSE    1000


int main()
{
    char sieve[ SIZE ];
    char *sp;
    int number;

    /* 将sieve[ SIZE ]初始化为 TRUE */
    for( sp = sieve; sp < &sieve[ SIZE ]; sp++ )
        *sp = TRUE;

    for( number = 3; ; number += 2 )
    {
        sp = &sieve[ 0 ] + ( number - 3 ) / 2;
        if ( sp > &sieve[ SIZE ] )
            break;

        while( sp += number, sp < &sieve[ SIZE ] )
            *sp = FALSE;
    }

    printf( "2\n" );

    for( number = 3, sp = &sieve[ SIZE ];
        sp < &sieve[ SIZE ];
        number += 2, sp++ )
    {
        if( *sp )
            printf( "%d\n", number );
    }

    return EXIT_SUCCESS;
}