Bjarne Stroustrup “Programming Principles and Practice Using C++” Chapter 12 Exercise 12
Using GUI library called FLTK (Fast Light Tool Kit, “full tick”).

Output: n = 2

Output: n = 1/2

Output: n = 3/2

Output: n = 4

// Philipp Siedler
// Bjarne Stroustrup's PP
// Chapter 12 Exercise 12
#define _USE_MATH_DEFINES
#include "Simple_window.h"
#include "Graph.h"
#include <cmath>
using namespace Graph_lib;
int main()
try
{
Point tl(100, 100);
Simple_window win(tl, 600, 400, "Regular Polygons");
Point center(win.x_max() / 2, win.y_max() / 2);
Graph_lib::Closed_polyline supEllipse;
supEllipse.set_color(Color::black);
double a = 100;
double y;
double b = 100;
double n; // 1/2; 3/2; 2; 4;
n = 4.0;
for (int x = - 100; x < 100; x++) {
y = b * pow(1 - pow(abs(x / a), n), 1 / n);
supEllipse.add(Point(x + center.x, y + center.y));
}
for (int x = 100; x > -100; x--) {
y = b * pow(1 - pow(abs(x / a), n), 1 / n);
y = -y;
supEllipse.add(Point(x + center.x, y + center.y));
}
win.attach(supEllipse);
win.wait_for_button();
}
catch (exception& e) {
cout << e.what() << endl;
return 1;
}
catch (...) {
cout << "Exiting" << endl;
return 2;
}