时间复杂度较高，但是简单易懂。

#include<iostream>
using namespace std;
const int maxl = 20;
int n = 1,a[maxl];
bool isprime(int m)
{
	if(m==1)return false;
	for(int i=2;i*i<=m;i++)if(m%i==0)return false;
	return true;
}
int main()
{
	while(cin>>a[n]&&a[n]!=0)n++;
	for(int i=1;i<=n-1;i++)
	{
		bool flag = 1;
		for(int j=3;j<=a[i]/2;j++)
		{
			if(isprime(j)&&isprime(a[i]-j))
			{
				cout<<a[i]<<" = "<<j<<" + "<<a[i]-j<<endl;
				flag = 0;
				break;
			}
		}
		if(flag)cout<<"Goldbach's conjecture is wrong\n";
	}
	return 0;
}