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 ans = 0, prev = 0;
        bool space = false;
        for(int i = 0; s[i] != NULL; ++i){
            if(s[i] == " ") {
                if(space == false)prev = ans, ans = 0, space = true;
                else continue;
            }else ans++, space = false;
        }
        if(ans == 0) return prev;
        return ans;
    }
};