I'm not a C++ guru, but for what they are worth, I have some comments:

• it would be better to evaluate s.end() just once (outside the loop)

• the function fails if s starts with a space

• you have duplicate code turning an int into a string. Perhaps use C++11 to_string or write your own a function, such as:

    template <typename T>
    static std::string to_string(T num)
    {
        stringstream ss;
        ss << num;
        return ss.str();
    }
  

I'm not a C++ guru, but for what they are worth, I have some comments:

• it would be better to evaluate s.end() just once (outside the loop). Correction: this won't help.

• the function fails if s starts with a space

• you have duplicate code turning an int into a string. Perhaps use C++11 to_string or write your own a function, such as:

    template <typename T>
    static std::string to_string(T num)
    {
        std::stringstream ss;
        ss << num;
        return ss.str();
    }