{C++} 대소문자 변환

#include <iostream>
#include <string>

using namespace std;

int main(void) {
    string str;
    cin >> str;
    for(int i = 0; i < str.size(); i++)
        if ('A' <= str[i] && str[i] <= 'Z'){
            // str[i] += 32;
            str[i] = tolower(str[i]);
        }else if ('a' <= str[i] && str[i] <= 'z'){
            // str[i] -= 32;
            str[i] = toupper(str[i]);
        }
    cout << str;
    return 0;
}