# right triangle class octagon [fltk]

Bjarne Stroustrup “Programming Principles and Practice Using C++”
Chapter 13 Exercise 14
Using GUI library called FLTK (Fast Light Tool Kit, “full tick”).

```Output:

```

[code language=”cpp”]
// Philipp Siedler
// Bjarne Stroustrup’s PP
// Chapter 13 Exercise 14

#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 operator-(Point& p1, Point& p2) {
Point p3 = Point(p1.x – p2.x, p1.y – p2.y);
return p3;
}

Point operator+(Point& p1, Point& p2) {
Point p3 = Point(p1.x + p2.x, p1.y + p2.y);
return p3;
}

double pointVecMag(Point vec) {
return sqrt(pow(vec.x, 2) + pow(vec.y, 2));;
}

struct Regular_triangle : Closed_polyline
{
Regular_triangle(Point origin, int edge, int height, Fl_Color linecolor)
: o(origin), e(edge), h(height), lc(linecolor)
{
generate_points();
};

void generate_points();
void draw_lines() const;

private:
Point o;
int e;
int h;
Fl_Color lc;
};

void Regular_triangle::generate_points()
{
add(Point(o.x + e / 2, o.y – h));
};

void Regular_triangle::draw_lines() const
{
fl_color(lc);
Closed_polyline::draw_lines();
};

{
Point origin_Pt1 = Regular_triangle::point(0) – Regular_triangle::point(2);
Point origin_Pt2 = Regular_triangle::point(1) – Regular_triangle::point(2);

Regular_triangle::set_point(0, rotated_Pt1 + Regular_triangle::point(2));
Regular_triangle::set_point(1, rotated_Pt2 + Regular_triangle::point(2));
};

int main()
try
{
Point tl(100, 100);
Simple_window win(tl, 720, 400, "Simple Window");
Point center(win.x_max() / 2, win.y_max() / 2);

int edge = 50;
int height = 0.5 * (1 + sqrt(2.0)) * edge; //r = 1/2 * ( 1 + sqrt(2)) * s

Vector_ref<Regular_triangle> rt;

for (int i = 0; i < 8; i++) {
rt.push_back(new Regular_triangle(center, edge, height, Fl_Color(i)));
rt[i].rotate_triangle(((2 * M_PI) / 8) * i);
win.attach(rt[i]);
}

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