LeetCode Add Binary

//  8ms
 1 class Solution {
public:
    string addBinary(string a, string b) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        reverse(a.begin(),a.end());
        reverse(b.begin(),b.end());
        int c=0;
        string s;
        int i;
        
        for(i=0;(i<a.size())&&(i<b.size());i++)
        {
            s.append(1,(char)((a[i]-'0'+b[i]-'0'+c)%2+'0'));
            c=(a[i]-'0'+b[i]-'0'+c)/2;
        }
        for(;i<a.size();i++)
        {
            s.append(1,(char)((a[i]-'0'+c)%2+'0'));
            c=(a[i]-'0'+c)/2;
        }
        for(;i<b.size();i++)
        {
            s.append(1,(char)((b[i]-'0'+c)%2+'0'));
            c=(b[i]-'0'+c)/2;
        }
        if(c==1)
            s.append(1,'1');
        reverse(s.begin(),s.end());
        return s;
    }
};