FLTK library and segmentation faults

Hiya, I am making a very simple app using the FLTK library, a dice
roller, thing is when I try to put text into the text output box I get
a segmentation fault, and I have never even heard of these, whats up
with my code?  Any help is muchly appreciated. Heres my code:



#include <FL/Fl.H>

#include <FL/Fl_Window.H>

#include <Fl/Fl_Value_Input.H>

#include <Fl/Fl_Button.H>

#include <Fl/Fl_Text_Display.H>

#include <Fl/fl_ask.H>

using namespace std;



//=====Start Window Class=====

class Window: public Fl_Window

{

    public:

        Window(int w, int h, const char* title);

        ~Window();

        //widget pointers

        Fl_Value_Input* Number;

        Fl_Value_Input* Sides;

        Fl_Value_Input* Coins;

        Fl_Button* Roll;

        Fl_Button* Flip;

        Fl_Text_Display* Output;

    private:

        //callback functions

        static void cb_roll(Fl_Button*, void*);

        void cb_roll_i(Fl_Button*, void*);

};

Window::Window(int w, int h, const char* title): Fl_Window(w, h, title)

{

    //Interface

    Fl_Value_Input* Number =

        new Fl_Value_Input(120, 20, 100, 20, "Number of die");

    Fl_Value_Input* Sides =

        new Fl_Value_Input(120, 60, 100, 20, "Number of sides");

    Fl_Value_Input* Coins =

        new Fl_Value_Input(120, 100, 100, 20, "Number Of Coins");

    Fl_Button* Roll =

        new Fl_Button(240, 40, 100, 20, "Roll Dice");

    Fl_Button* Flip =

        new Fl_Button(240, 100, 100, 20, "Flip Coins");

    Fl_Text_Display* Output =

        new Fl_Text_Display(10, 140, 330, 250, "");

    //Callbacks

    Roll->callback((Fl_Callback*) cb_roll, this);

}

Window::~Window()

{

    //do nothing deconstructor

}

void Window::cb_roll(Fl_Button* o, void* v)

{

    Window* T=(Window*)v;

    T->cb_roll_i(o,v);



}

void Window::cb_roll_i(Fl_Button*, void*)

{

    Output->insert("Test");

}

//=====End Window Class=====



int main(int argc, char* argv[])

{

    Window main(350, 400, "Dice Roller");

    main.show();

    

    return Fl::run();

}