adding lab 3

labs/03_debugging/line.h

@@ -0,0 +1,29 @@
+#include "point.h"
+
+// A simple line class.  In this simple world, we'll follow the
+// convention often used in Computer Graphics.  y is the vertical
+// axes, "pointing" up.  The x and z axes define the ground plane.
+
+class Line {
+public:
+  Line(const Point &a_, const Point &b_) : a(a_),b(b_) {}
+  const Point& get_a() const { return a; }
+  const Point& get_b() const { return b; }
+private:
+  Point a,b;
+};
+
+
+// A helper function to print a Line.
+std::ostream& operator<< (std::ostream &ostr, const Line &l);
+
+
+// A helper function to gradient of a line.
+double gradient(const Line &ln);
+
+
+// A helper function to compare the gradient of two Lines.
+// (That can be used to sort a collection of roads.)
+bool steeper_gradient(const Line &m, const Line &n);
+
+