form.cpp

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#include "form.h"
 
#include <iostream>
using namespace std;
 
// keep the CLANG compiler silent (it is right!)
//  https://stackoverflow.com/questions/28786473/clang-no-out-of-line-virtual-method-definitions-pure-abstract-c-class
Form::~Form() {}
 
float Quadrat::area() const
{
    return _edge * _edge;
}
 
float Circle::area() const
{
    return static_cast<float>(M_PI) * _radius * _radius;
}
 
bool operator<(const Form &a, const Form &b)
{
    return a.area() < b.area();
}
 
bool kleiner (const Form *a, const Form *b)
{
    return a->area() < b->area();                      // uses  operator<(const Form &a, const Form &b)
}
 
//  Output-Operator : Here we benefit from polymorphism
ostream &operator<<(ostream &s, const Form &rhs)
{
    s << rhs.classname() << " with centre ";
    s << "(" << rhs.GetX() << "," << rhs.GetY() << ")";
    s << " has an area of " << rhs.area();
    return s;
}