int alen = a.size();

int blen = b.size();

bool carry = false;

string result;

while( alen>0 || blen>0) {

int abit = alen<=0 ? 0 : a[alen-1]-'0';

int bbit = blen<=0 ? 0 : b[blen-1]-'0';

int cbit = carry ? 1 : 0;

result.insert(result.begin(), '0' + ((abit+bbit+cbit) & 1) );

carry = (abit+bbit+cbit>1);

alen--; blen--;

}

if (carry){

result.insert(result.begin(), '1');

}

return result;

{

string a = "11";

string b = "1";

if (argc>2){

a = argv[1];

b = argv[2];

}

cout << a << "+" << b << "=" << addBinary(a, b) << endl;