各位請看一下:

#include <iostream>
using namespace std;

int main(){
    int a[168] = {2, 3}, i, n, j;
    for (i = 2, n = 6; n <= 1000; n += 6){
        for (j = 0; j < i; j++) if (!((n-1) % a[j])) break;
        if (j == i) a[i++] = n - 1;
        for (j = 0; j < i; j++) if (!((n+1) % a[j])) break;
        if (j == i) a[i++] = n + 1;
    }
    while (cin >> n, n)
          if (n == 2 || n == 3) cout << 0 << endl;
          else if (n%6 == 1 && n != 1 || n%6 == 5){
               for (i = 0; a[i] * a[i] <= n; i++)
                   if (!(n % a[i])) {cout << 1 << endl; break;}
               if (a[i] * a[i] > n) cout << 0 << endl;
          }
          else cout << 1 << endl;
}