LeetCode-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) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        int count=0;
        int lastcount=0;
        if(s==NULL)return 0;
        bool begin=false;
        int i=0;
        while(s[i]!=''){
            if(!begin){
                if(s[i]>='a'&&s[i]<='z'||s[i]>='A'&&s[i]<='Z'){
                    count++;
                    begin=true;
                }
            }
            else{
                if(s[i]>='a'&&s[i]<='z'||s[i]>='A'&&s[i]<='Z'){
                    count++;
                }
                else{
                    if(s[i]=='')return count;
                    else{
                        lastcount=count;
                        count=0;
                        begin=false;
                    }
                }
            }
            i++;
        }
        if(begin)return count;
        return lastcount;
    }
};