#include<iostream> #include<cstdlib> #include<cmath> using namespace std;

class point { private: double x,y; public: point(double xx=0,double yy=0){x=xx;y=yy;} friend void triangle(point &,point &,point &); friend istream &operator>>(istream &,point &); };

void triangle(point &p1,point &p2,point &p3) { double k=sqrt((p1.x-p2.x)*(p1.x-p2.x)+(p1.y-p2.y)*(p1.y-p2.y)); double l=sqrt((p1.x-p3.x)*(p1.x-p3.x)+(p1.y-p3.y)*(p1.y-p3.y)); double s=sqrt((p3.x-p2.x)*(p3.x-p2.x)+(p3.y-p2.y)*(p3.y-p2.y)); if(k+l>s && k-l<s) { double m=(k*k+l*l-s*s)/(2*k*l); //ÕâÀïÓ¦¸Ã×¢Òâһϣ¬Ò»¶¨ÒªÀ¨ºÅ cout<<"Äܹ¹³ÉÈý½ÇÐΣ¬Ãæ»ýΪ£º"<<0.5*k*l*sqrt(1-m*m)<<endl; } else cout<<"²»Äܹ¹³ÉÈý½ÇÐÎ"<<endl; } istream &operator>>(istream &input,point &p) { input>>p.x>>p.y; // here is an error, instead of cin, you should set the parameter input as istream object return input; }

int main() { point p1,p2,p3; cout<<"ÇëÊäÈëÈý¸öµã£º"; cin>>p1>>p2>>p3; triangle(p1,p2,p3); system("pause");

return 0; }