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+// File: fractal.cxx

+// A demonstration program for the random_fractal function from Chapter 9.

+

+#include <cassert>    // Provides assert

+#include <cstdlib>    // Provides EXIT_SUCCESS

+#include <iostream> // Provides cin, cout

+#include "useful.h"   // From Appendix H. Provides random_real, display

+using namespace std;

+

+// PROTOTYPE for the function used in this demonstration program.

+void random_fractal

+(double left_height, double right_height, double width, double epsilon);

+// Precondition: width and epsilon are both positive.

+// Postcondition: The function has generated a random fractal from a line

+// segment. The parameters left_height and right_height are the heights of the

+// two endpoints of the line segment, and the parameter width is the segment's

+// width. The generation of the random fractal stops when the width of the

+// line segments reaches epsilon or less.

+// Method of displaying the output: The height of the right endpoint of

+// each line segment in the random fractal is displayed by calling the

+// function display(...).

+

+int main()

+{

+    cout << "Turn your head sideways to see a nice landscape:" << endl;

+    random_fractal(0, 0, 16, 1);

+    return EXIT_SUCCESS;

+}

+

+void random_fractal

+(double left_height, double right_height, double width, double epsilon)

+// Library facilities used: cassert, useful.h (From Appendix I).

+{

+    double mid_height;   // Height of the midpoint of the line segment

+

+    assert(width > 0);

+    assert(epsilon > 0);

+

+    if (width <= epsilon)

+        	display(right_height);

+    else

+    {

+        mid_height = (left_height + right_height) / 2;

+        	mid_height += random_real(-width, width);

+        	random_fractal(left_height, mid_height,   width/2, epsilon);

+        	random_fractal(mid_height,  right_height, width/2, epsilon);

+    }

+}