【C++】字符串的大小写转换

#include<string>
#include<algorithm>
#include<iostream>

using namespace std;

int main(){
    string s = "abcABC";
    transform(s.begin(), s.end(), s.begin(), ::tolower);

    cout << s << endl; //"abcabc"
    
    string upper;
    upper.resize(s.size());
    transform(s.begin(), s.end(), upper.begin(), ::toupper);
    cout << s << endl; //"abcabc"
    cout << upper << endl; //"ABCABC"

    return 0;
}