HDU-2161 Primes

　　这里主要预习了素数筛选以及输入外挂的编写。涛神的筛选法一直记着，给力。

　　

#include <cstdio>
#include <cstring>
#include <cstdlib>
using namespace std;

char hash[16005] = {0};

bool getint( int &t )
{
    char c;  int f = 1;
    while( c = getchar(), c != '-' && ( c < '0' || c > '9' ) )
    {
        if( c == EOF )
            return false;
    } 
    if( c == '-' )
        f = -1;
    else
        t = c - '0';
    while( c = getchar(), c >= '0' && c <= '9' )
        t = t * 10 + c -'0';
    t *= f;
    return true;
}

int main()
{
    hash[1] = 1;
    for( int i = 2; i <= 16000; i += 2 )
        hash[i] = 1;
    for( int i = 3; i <= 301; ++i )
    {
        int k = 2 * i;
        for( int j = i * i; j <= 16000; j += k )
        {
            hash[j] = 1;
        }
    }
    int N, t = 1;
    while( getint( N ), N> 0 )
    {
        printf( hash[N] ? "%d: no\n" : "%d: yes\n", t );
        t++;
    }    
    return 0;
}