restructure and add ipi texs

ws2019/ipi/uebungen/cpp_headers/shape.cc

@@ -0,0 +1,69 @@
+#include<iostream>
+#include<cmath>
+
+const double pi = 3.1415926536;
+
+class Shape
+{
+public:
+  virtual ~Shape () {};
+  virtual double area () = 0;
+  virtual double diameter () = 0;
+  virtual double circumference () = 0;
+};
+
+// works on every shape 
+double circumference_to_area (Shape &shape) {
+  return shape.circumference()/shape.area();
+}
+
+class Circle : public Shape {
+public:
+  Circle (double r) {radius = r;}
+  virtual double area () {
+    return pi*radius*radius;
+  }
+  virtual double diameter () {
+    return 2*radius;
+  }
+  virtual double circumference () {
+    return 2*pi*radius;
+  }
+private:
+  double radius;
+};
+
+class Rectangle : public Shape {
+public:
+  Rectangle (double aa, double bb) {
+    a = aa; b = bb;
+  }
+  virtual double area () {return a*b;}
+  virtual double diameter () {
+    return sqrt(a*a+b*b);
+  }
+  virtual double circumference () {
+    return 2*(a+b);
+  }
+private:
+  double a, b;
+};
+
+int main ()
+{
+  Rectangle unit_square(1.0, 1.0);
+  Circle unit_circle(1.0);
+  Circle unit_area_circle(1.0/sqrt(pi));
+
+  std::cout << "Das Verhältnis von Umfang zu Fläche beträgt\n";
+  std::cout << "Einheitsquadrat:    "
+	    << circumference_to_area(unit_square) 
+	    << std::endl;
+  std::cout << "Kreis mit Fläche 1: "
+	    << circumference_to_area(unit_area_circle) 
+	    << std::endl;
+  std::cout << "Einheitskreis:      "
+	    << circumference_to_area(unit_circle) 
+	    << std::endl;
+  return 0;
+}