vector operator+=

vector &vector::operator+=(const vector &w)
{
    // To Do
    //
    // Add the vector "w" to this vector.  Note that we have to return this vector once we
    // are done to support c++ statement such as v0 = v1 = v2.
    int i = 0;
    while (this) {
        v[i] += w.v[i];
        i++;
    }
    return *this;
}