C++中的auto的使用

string s = "hello";
for (auto &i : s ) 
    i = toupper(i); //改变成大写，影响s的值
cout<<s<<endl; //s的值是 HELLO

string s = "hello";
for (auto i : s )
    i = toupper(i); //改变成大写，不影响s的值
cout<<s<<endl; //s的值是 hello

#include <iostream>
#include <map>

using namespace std;

int main() {
    map<int,string> student;
    student.insert(pair<int,string>(2,"li"));
    student.insert(pair<int,string>(1,"wang"));
    student.insert(pair<int,string>(3,"sun"));
    for(auto &v : student) // for(auto v : student)也是可以的
        cout<<"key: "<<v.first<<" | value: "<<v.second<<endl;
    return 0;
}