709. 转换成小写字母(c++)

class Solution {
public:
    string toLowerCase(string s) {
        for(char& ch:s){
            ch = tolower(ch);
        }
        return s;
    }
};

class Solution {
public:
    string toLowerCase(string s) {
        for(char& ch:s){
            if(ch >= 65 && ch <= 90){
                ch = ch|32;//位运算
            }         
        }
        return s;

    }
};

class Solution {
public:
    string toLowerCase(string s) {
        for(char& ch:s){
            if(ch >= 65 && ch <= 90){
                ch = ch+32;
            }           
        }
        return s;
    }
};