TZOJ5255: C++实验：三角形面积

#include<iostream>
#include<iomanip>
#include<math.h>
#include<cmath>
using namespace std;
class CPoint
{
   public:
   int x,y;
   CPoint(int x=0,int y=0):x(x),y(y){}
   friend istream &operator>>(istream &is,CPoint &p)
   {
       is>>p.x>>p.y;
       return is;
   }

};
class CTriangle
{
   public:
   CPoint p1,p2,p3;
   CTriangle(CPoint p1,CPoint p2,CPoint p3):p1(p1),p2(p2),p3(p3){}
   double Area()
   {
       double a=sqrt((p1.x-p2.x)*(p1.x-p2.x)+(p1.y-p2.y)*(p1.y-p2.y));
       double b=sqrt((p1.x-p3.x)*(p1.x-p3.x)+(p1.y-p3.y)*(p1.y-p3.y));
       double c=sqrt((p3.x-p2.x)*(p3.x-p2.x)+(p3.y-p2.y)*(p3.y-p2.y));
       double p=(a+b+c)/2.0;
       double s=sqrt(p*(p-a)*(p-b)*(p-c));
       return s;
   }
};