Add Binary

Given two binary strings, return their sum (also a binary string).

For example,
a = "11"
b = "1"
Return "100".

思路：学习这种代码的简洁写法。

class Solution {
public:
    string addBinary(string a, string b) {
        string res;
        int ia = a.size() - 1, ib = b.size() - 1, c = 0;
        while (ia >= 0 || ib >= 0 || c == 1)
        {
            c += (ia >= 0) ? (int)(a[ia--] - '0') : 0;
            c += (ib >= 0) ? (int)(b[ib--] - '0') : 0;
            res = (char)(c % 2 + '0') + res;
            c = c >> 1;
        }
        return res;
    }
};