# quadratic function – parabola graphing 5/8 [fltk]

Bjarne Stroustrup “Programming Principles and Practice Using C++”
Chapter 15 Shape Graphing Drill 6
Using GUI library called FLTK (Fast Light Tool Kit, “full tick”).

Output:

[code language=”cpp”]
// Philipp Siedler
// Bjarne Stroustrup’s PP
// Chapter 15 Shape Graphing Drill 6

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

using namespace Graph_lib;

constexpr int xmax = 600;
constexpr int ymax = 600;

constexpr int x_orig = xmax / 2;
constexpr int y_orig = ymax / 2;
Point orig(x_orig, y_orig);

constexpr int r_min = -10;
constexpr int r_max = 10;

constexpr int n_points = 400;

constexpr int x_scale = 20;
constexpr int y_scale = 20;

// layout
constexpr int xoffset = 100;
constexpr int yoffset = 100;

constexpr int xspace = 100;
constexpr int yspace = 100;

constexpr int xlength = xmax – xoffset – xspace;
constexpr int ylength = ymax – yoffset – yspace;

double one(double x) { return 1; }
double slope(double x) { return x / 2; }
double square(double x) { return pow(x, 2); }

int main()
try
{
Point tl(100, 100);
Simple_window win(tl, xmax, ymax, "Function graphs.");

Axis x(Axis::x, Point(orig.x – 200, orig.y), 400, 20, "1 == 20");
x.set_color(Color::red);

Axis y(Axis::y, Point(orig.x, orig.y + 200), 400, 20, "1 == 20");
y.set_color(Color::red);

Function f1(square, r_min, r_max, orig, n_points, x_scale, y_scale);
f1.set_color(Color::black);

Text f1_label(Point(xoffset, orig.y + 40), "pow(x,2)");

win.attach(f1);
win.attach(f1_label);

win.attach(x);
win.attach(y);

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