LintCode "Binary Representation"

Not hard to think of a solution. But the key is all details.

class Solution {

public:
    /**
     *@param n: Given a decimal number that is passed in as a string
     *@return: A string
     */
    string binaryRepresentation(string n) {
        size_t pos = n.find(".");
        unsigned long vi = atoi(n.substr(, pos).c_str());
        double vf = atof(n.substr(pos).c_str());

        //  Int part
        string si;
        while(vi)
        {
            si = ((vi & ) ? '' : '') + si;
            vi >>= ;
        }
        if(si.empty()) si = "";
        if(vf == .) return si;

        //  Fractional part
        string sf;
        while (vf > 0.0)
        {
            if (sf.length() > ) return "ERROR";
            if (vf >= 0.5) {
                sf += '';
                vf -= 0.5;
            }
            else
            {
                sf += '';
            }
            vf *= ;
         }
        return si + "." + sf;
    }
};