题目是验证哥德巴赫猜想= =
#include<stdio.h>
#include<math.h>
int ig(int n)
{
    int i,count=0;
    double a=sqrt(n);
    for(i=2;i<=a;i++)
        if(n%i==0)
            count++;
    if(count)
        return 0;
    else
        return 1;   
}
int main()
{
    int n,a,b,i;
    while(scanf("%d",&n)!=EOF,n>=6&&n<=2000000000&&n%2==0)
    {
        a=b=n/2;
        if(ig(a)&&ig(b))
            printf("%d %d\n",a,b);
        else
        {
            for(;ig(a)==0||ig(b)==0;a--,b++);
            printf("%d %d\n",a,b);
        }                    
    }
    return 0;
}

明白了，感谢。