leetcode 709. To Lower Case

Implement function ToLowerCase() that has a string parameter str, and returns the same string in lowercase.

Example 1:

Input: "Hello"
Output: "hello"

Example 2:

Input: "here"
Output: "here"

Example 3:

Input: "LOVELY"
Output: "lovely"

 1 class Solution {
 2 public:
 3     string toLowerCase(string str) {
 4         string res;
 5         for (int i = 0; i < str.length(); i++) {
 6             if (str[i] >= 'A' && str[i] <= 'Z') {
 7                 res += 'a' + (str[i] - 'A');
 8             } else {
 9                 res += str[i];
10             }
11         }
12         return res;
13     }
14 };