poj 2262 Goldbach's Conjecture

 1 #include<cstdio>
 2 #include<memory.h>
 3 #define maxn 5000005
 4 int prime[maxn];
 5 void f()
 6 {
 7     memset(prime,0,sizeof(prime));
 8     prime[0] = prime[1] = 0;
 9     for(int i = 2; i < maxn; i++)
10     {
11         if(!prime[i])
12         {
13             for(int j = 2 * i; j < maxn; j += i)
14                 prime[j] = 1;
15         }
16     }
17 }
18 int main()
19 {
20     freopen("input.txt","r",stdin);
21     int n,i;
22     f();
23     while(scanf("%d",&n) && n)
24     {
25         for(i = 3; i < n /2; i += 2)
26         {
27             if(!prime[i] && !prime[n - i])
28                 break;
29         }
30         printf("%d = %d + %d\n",n,i,n-i);
31     }
32     return 0;
33 }