【报错】9.22 题目中,应该同时修改 mid 的值，否则也会失效

``` c++
int main()
{
	vector<int> iv = { 1,2,3,4,5,6,7,8 };
	vector<int>::iterator iter = iv.begin(),
		mid = iv.begin() + iv.size() / 2;
	while (iter != mid)
	{
		if (*iter == 3)
		{
			iter = iv.insert(iter, 2 * 3);
			++iter;
			mid = iv.begin() + iv.size() / 2;
		}
		++iter;
	}

    return 0;
}
```