[leetcode-67-Add Binary]

Given two binary strings, return their sum (also a binary string).
For example,
a = "11"
b = "1"
Return "100".

思路：

模拟加法时候的情形，从最后一位开始进行相加，注意进位的情况。

string addBinary(string a, string b)
    {
        int aIndex = a.size() - 1, bIndex = b.size() - 1;
        int numa = 0, numb = 0, carry = 0, temp = 0;
        string c;
        char tempChar[10];
        while (aIndex >= 0 || bIndex >= 0 || carry == 1)//简洁一些了
        {
            numa = 0, numb = 0;
            if(aIndex >= 0)numa = a[aIndex--] - '0';
            if(bIndex >= 0)numb = b[bIndex--] - '0';
            temp = numa + numb + carry;
            if (temp > 1)
            {
                carry = 1;
                temp = temp - 2;
            }
            else carry = 0;            
            sprintf(tempChar, "%d", temp);        
            c.insert(0, tempChar);            
        }
        return c;
    }