# ellipse foci class [fltk]

Bjarne Stroustrup “Programming Principles and Practice Using C++”
Chapter 13 Exercise 11
Using GUI library called FLTK (Fast Light Tool Kit, “full tick”).

```Output:

```

[code language=”cpp”]
// Philipp Siedler
// Bjarne Stroustrup’s PP
// Chapter 13 Exercise 11

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

using namespace Graph_lib;

ostream& operator<<(ostream& out, Point& a) {
out << "(" << a.x << "," << a.y << ")";
return out;
}

Point ptOnEllipse(Graph_lib::Ellipse& e, double p) {
int a = e.major(); //width
int b = e.minor(); //height

int x = e.center().x + a * cos(M_PI * 2 * p);
int y = e.center().y – b * sin(M_PI * 2 * p);

return Point(x, y);
}

int main()
try
{
Point tl(100, 100);
Simple_window win(tl, 1000, 800, "Simple Window");
Point center(win.x_max() / 2, win.y_max() / 2);

//Ellipse
Graph_lib::Ellipse myEllipse(center,300, 200);
myEllipse.set_color(Color::red);
//Foci
Mark focus1(myEllipse.focus1(), ‘x’);
focus1.set_color(Color::red);
Mark focus2(myEllipse.focus2(), ‘x’);
focus2.set_color(Color::red);
//Pt on Ellipse
double ptParameter = 0.7;
Point pt = ptOnEllipse(myEllipse, ptParameter);
Mark markOnEllipse(pt, ‘x’);
markOnEllipse.set_color(Color::red);

//Lines
Lines fociLines;
fociLines.set_color(Color::blue);

//xyAxis
Axis xa(Axis::x, center, 400, 20, "x axis");
xa.set_color(Color::black);
Axis ya(Axis::y, center, 300, 15, "y axis");
ya.set_color(Color::black);

win.attach(myEllipse);
win.attach(focus1);
win.attach(focus2);
win.attach(markOnEllipse);
win.attach(fociLines);
win.attach(xa);
win.attach(ya);

win.wait_for_button();
}
catch (exception& e) {
cout << e.what() << endl;
return 1;
}
catch (…) {
cout << "Exiting" << endl;
return 2;
}
[/code]