接上节内容，反向迭代器（aoto的价值显示的更明显）
int main()
{string s1("hello world");//string::reverse_iterator rit = s1.rbegin();auto rit = s1.rbegin();while (rit != s1.rend()){(*rit) += 3;cout << *rit << " ";++rit;}cout << endl;cout << s1 << endl;Func(s1);return 0;
}
这里就凸显的范围for 不能倒着遍历，只能正着遍历
四种迭代器：iterator,const_iterator,reverse_iterator,const_reverse_iterator
