class BaseClass {
    public:
        BaseClass(int x);
        int getX() { return x_; }
    private:
        int x_;
};
class SubClass : public BaseClass {
    public:
        SubClass(int x, int y);
    private:
        int y_;
};
BaseClass::BaseClass(int x) : x_(x) {}
SubClass::SubClass(int x, int y) : BaseClass(x), y_(y) {}