字符串大小写转换：C++ 代码实现

#include <iostream>
#include <string>
using namespace std;

int main() {
    string str;
    cin >> str;

    for (int i = 0; i < str.length(); i++) {
        if (str[i] >= 'a' && str[i] <= 'z') {
            str[i] = toupper(str[i]);
        } else if (str[i] >= 'A' && str[i] <= 'Z') {
            str[i] = tolower(str[i]);
        }
    }

    cout << str << endl;

    return 0;
}