编程实现：三角形种类判定与面积计算

#include<iostream>
#include<math.h>
using namespace std;
class point
{ protected:
    double x,y;
public:
double get_x();  //得到X坐标
double get_y();  //得到Y坐标
point(double,double);
point(){}       //无参构造函数
};
point::point(double a,double b){x=a;y=b;}
double point::get_x(){return x;}  //得到X坐标
double point::get_y(){return y;}  //得到Y坐标
class line:public point
{ private:
    point p1;
public:
line(double , double , double , double );
double dis(); //两点之间直线的距离
line(){}      //无参构造
};
line::line(double a, double b, double c, double d):point(a,b),p1(c,d){}
double line::dis()//两点之间直线的距离
{     return sqrt(pow((get_x()-p1.get_x()),2)+pow((get_y()-p1.get_y()),2));   }
//三角形类
class triangle
{ private:
line l1,l2,l3;