Length of Last Word

Given a string s consists of upper/lower-case alphabets and empty space characters ' ', return the length of last word in the string.
If the last word does not exist, return 0.
Note: A word is defined as a character sequence consists of non-space characters only.
For example,
Given s = "Hello World",
return 5.

class Solution {
public:
    int lengthOfLastWord(const char *s) {
        int res = 0;
        int length = strlen(s);
        for(int i = length-1; i >= 0; i--) {
            if(s[i] != ' ') 
                res++;
            else if(res > 0) 
                break;
        }
        return res;
    }
};