Problem C: 平面上的点和线——Point类、Line类 (III)

#include <iostream>
using namespace std;
class Point
{
private:
    double st,ed;
public:
    Point():st(0),ed(0){cout << "Point : (" <<st<< ", " <<ed<<") is created." << endl;}
    Point(double stt ,double edd ):st(stt),ed(edd){cout << "Point : (" <<st<< ", " <<ed<<") is created." << endl;}
    Point (const Point &p)
 {st = p.st;ed= p.ed;cout << "Point : (" << st<< ", " << ed<<") is copied." << endl;}
    double x() const {return st;}
    double y() const {return ed;}
    void show()
    {
        cout << "Point : (" <<st<< ", "<<ed<< ")" <<endl;
    }
    ~Point ()
  {
      cout << "Point : (" <<st<< ", " <<ed <<") is erased." << endl;
  }
};
class Line
{
private :
    Point st_,ed_;
public:
  Line( Point &sst, Point &eed):st_(sst),ed_(eed)
    { cout << "Line : (" << st_.x() << ", " << st_.y()<< ") to (" <<ed_.x() <<", " << ed_.y() << ")" << " is created." << endl;}
    Line(double x1,double y1,double x2,double y2):st_(x1,y1),ed_(x2,y2)
    {
   cout << "Line : (" << st_.x() << ", " << st_.y()<< ") to (" <<ed_.x() <<", " << ed_.y() << ")" << " is created." << endl;
    }
    void show() const
    {cout << "Line : (" << st_.x() << ", " << st_.y()<< ") to (" <<ed_.x() <<", " << ed_.y() << ")" <<endl;
    }
    ~Line()
    {
       cout << "Line : (" << st_.x() << ", " << st_.y()<< ") to (" <<ed_.x() <<", " << ed_.y() << ")" << " is erased." << endl;
    }
};
int main()
{
    char c;
    int num, i;
    double x1, x2, y1, y2;
    Point p(1, -2), q(2, -1), t;
    t.show();
    std::cin>>num;
    for(i = 1; i <= num; i++)
    {
        std::cout<<"=========================\n";
        std::cin>>x1>>c>>y1>>x2>>c>>y2;
        Line line(x1, y1, x2, y2);
        line.show();
    }
    std::cout<<"=========================\n";
    Line l1(p, q), l2(p, t), l3(q, t), l4(t, q);
    l1.show();
    l2.show();
    l3.show();
    l4.show();
}