# draw a binary tree [fltk]

Bjarne Stroustrup “Programming Principles and Practice Using C++”
Chapter 14 Exercise 11
Using GUI library called FLTK (Fast Light Tool Kit, “full tick”).

```Output:

```

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

class Binary_tree : public Shape
{
public:
Binary_tree(Point root, int levels)
:r(root), l(levels)
{
initialize_nodes();
}
~Binary_tree() {}

void initialize_nodes();
void draw_lines() const;

private:
Point r;
int l;
vector<Point> node_points;

};

void Binary_tree::initialize_nodes()
{
double nodes = 1.0;

double tree_w = l * 100;

for (int i = 0; i < l; i++) {
for (double j = -(nodes / 2); j < (nodes / 2); j++) {
if (i == 0) {
node_points.push_back(Point(r.x + j, r.y + i * 30));
}
else {
node_points.push_back(Point(r.x + (double(tree_w / nodes) / 2) + (j * double(tree_w / nodes)), r.y + i * 30));
}
}
nodes *= 2;
}
}

void Binary_tree::draw_lines() const
{
// draw nodes
for (int i = 0; i < node_points.size(); i++) {
Circle c(node_points[i], 5);
c.set_style(Line_style(Line_style::solid, 2));
c.draw();
}

// draw connecting lines
int node = 2;

for (int i = 0; i < node_points.size() – ((node_points.size() + 1) / 2); i++) {
for (int j = 1; j < 3; j++) {

Point from(node_points[i].x, node_points[i].y + 5);
Point to(node_points[i * node + j].x, node_points[i * node + j].y – 5);

Line(from, to).draw();
}
}
}

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);

Binary_tree tree(Point(center.x, 20), 7);
tree.set_color(Color::red);

win.attach(tree);

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