Add Binary

"11"

"1"

"100"

string addBinary(string a, string b) {
//4ms
const char * shortStr = (a.size()<=b.size())?a.c_str():b.c_str();
const char * longStr = (a.size()>b.size())?a.c_str():b.c_str();
int lenShort = strlen(shortStr);
int lenLong = strlen(longStr);

string s="";
int temp;
int flag = 0;
for (int i = 0; i < lenShort; ++i)
{
temp = shortStr[lenShort-1-i]-'0'+longStr[lenLong-1-i]-'0'+ flag;
flag = temp/2;
s.insert(0,1,'0'+temp%2);
}

for (int i = lenLong-1-lenShort; i >=0; --i)
{
temp = longStr[i]-'0'+flag;
flag = temp/2;
s.insert(0,1,'0'+temp%2);
}

if (flag == 1)
s.insert(0,1,'1');
return s;
}