0521-1 三角形類別的異常處理

/* PRESET CODE BEGIN - NEVER TOUCH CODE BELOW */

#include <iostream>
#include<iomanip>
#include <cmath>
#include<string>
using namespace std;
const double TOL = 1e-10;
class ERR{    //異常處理
  public:
    string msg(){
        return "retry";
    }
};
class Point{    //xy座標類別
  private:
    double x, y;
  public:
    Point(double a = 0., double b = 0.):x(a), y(b){}
    double getx() {return x;}
    double gety() {return y;}
    friend istream& operator>> (istream& in, Point& pt);

};

istream& operator>> (istream& in , Point& pt){
    return in >> pt.x >> pt.y;
}


class Triangle{    //三角形
  private:
    Point pt1, pt2, pt3;
  public:
    Triangle(Point& p, Point& q, Point& r) throw(ERR)
        :pt1(p), pt2(q), pt3(r){
        if(area() < TOL) throw ERR();
    }
    double area();  //待完成
    double perimeter();  //待完成
    friend ostream& operator<< (ostream& out, Triangle& foo);  //待完成
};

int main(){
    Point a, b, c;
    while(1){
        try{
            cin >> a >> b >> c;
            Triangle foo(a,b,c);
            cout << foo << endl;
            break;
        }
        catch (ERR& err){
            cout << err.msg() << endl;
        }
    }
    return 0;
}

/* PRESET CODE END - NEVER TOUCH CODE ABOVE*/
double distance(double x1,double y1,double x2,double y2)
{
    double distance=sqrt(pow(x2-x1,2)+pow(y2-y1,2));
    return distance;
}

ostream& operator<< (ostream& out, Triangle& foo)
{
    cout<<fixed<<setprecision(2)<<"area = "<<foo.area()<<endl<<"perimeter = "<<foo.perimeter();
}

double Triangle::area()
{
    double a=distance(this->pt1.getx(),this->pt1.gety(),this->pt2.getx(),this->pt2.gety());
    double b=distance(this->pt1.getx(),this->pt1.gety(),this->pt3.getx(),this->pt3.gety());
    double c=distance(this->pt3.getx(),this->pt3.gety(),this->pt2.getx(),this->pt2.gety());
    double s= (a+b+c)/2;
    return sqrt(s*(s-a)*(s-b)*(s-c));
}

double Triangle::perimeter()
{
    double a=distance(this->pt1.getx(),this->pt1.gety(),this->pt2.getx(),this->pt2.gety());
    double b=distance(this->pt1.getx(),this->pt1.gety(),this->pt3.getx(),this->pt3.gety());
    double c=distance(this->pt3.getx(),this->pt3.gety(),this->pt2.getx(),this->pt2.gety());
    return a+b+c;
}

/*
輸入說明:
         輸入三個點的x,y座標，x和y之間用空格隔開，每個點之間用空格隔開。

輸出說明:
         若三個點無法構成確切的三角形，則輸出 ”retry” (retry輸出後須換行)，
         並重新輸入三個點直到可以構成三角形。可構成三角形後輸出該三角形的面積與周長

註：輸出結果用四捨五入取小數點第二位
SAMPLE INPUT
          1 1 2 2 3 3↵
          1 1 1 2 2 2↵
SAMPLE OUTPUT
          retry↵
          area = 0.50↵
          perimeter = 3.41↵
*/