randomly moving shape [fltk]

Bjarne Stroustrup “Programming Principles and Practice Using C++”
Chapter 16 Exercise 5
Using GUI library called FLTK (Fast Light Tool Kit, “full tick”).

```Output:

```

[code language=”cpp”]
// Philipp Siedler
// Bjarne Stroustrup’s PP
// Chapter 16 Exercise 5

#define _USE_MATH_DEFINES
#include "Simple_window.h"
#include "Graph.h"
#include <cmath>
#include "GUI.h"

// layout
constexpr int xmax = 400;
constexpr int ymax = 400;

struct My_window : Window {
My_window(Point xy, int w, int h, const string& title, string url)
: Window(xy, w, h, title),
next_button_pushed(false),
next_button(Point(x_max() – 140, 0), 70, 20, "Next", cb_next),
quit_button(Point(x_max() – 70, 0), 70, 20, "Quit", cb_quit),
url(url),
counter(0)
{
attach(next_button);
attach(quit_button);

// open input stream
ifstream ist(url);
int input_x;
char comma;
int input_y;

// store data in vectors
while (ist >> input_x >> comma >> input_y)
{
in_x.push_back(input_x);
in_y.push_back(input_y);
}
}

void wait_for_button()
{
while (!next_button_pushed) Fl::wait();
next_button_pushed = false;
Fl::redraw();
}

Button next_button;
Button quit_button;

private:
bool next_button_pushed;
string url;
int counter;
Vector_ref<Shape> s;

vector<int> in_x;
vector<int> in_y;

{
}

{
}

void next();
void quit() { hide(); }
};

void My_window::next()
{
if (s.size() < in_x.size())
{
if (s.size() != 0) { detach(s[s.size() – 1]); }
s.push_back(new Circle(Point(in_x[counter], in_y[counter]), 20));
attach(s[s.size() – 1]);
redraw();
counter++;
}
}

int main()
try
{
My_window win(Point(100, 100), xmax, ymax + 20, "next buttons window", "Data/point_sequence.txt");
return gui_main();
}
catch (exception& e) {
cerr << "error: " << e.what() << ‘\n’;
keep_window_open();
return 1;
}
catch (…) {
cerr << "Unknown exception!\n";
keep_window_open();
return 2;
}
[/code]