HDU 1397 Goldbach's Conjecture

#include<stdio.h>
#include<string.h>
#define max 1 << 15 + 1
int num[max + 5],n;
void fun(  )
{
     memset( num,0,sizeof( num ) );
     num[0] = num[1] = 1;
     for( int i = 2; i <= max / 2; ++i )
          if( !num[i] )
              for( int j = i + i; j <= max; j += i )
                   num[j] = 1;
}
int cal( )
{
    int sum = 0;
    for( int i = 2; i <= n / 2; ++i )
         if( !num[i] && !num[n-i] )
             ++sum;
    return sum;
}
int main(  )
{
    fun(  );
    while( scanf( "%d",&n ),n )
           printf( "%d\n",cal(  ) );
    return 0;
}