麻烦各位大侠看下这个问题，有关c++的，我太菜了

#include
#include
using namespace std;

class point
{
protected:
double x1,y1;
public:
point(double a,double b)
{
x1=a;
y1=b;
}
~point()
{}
virtual void display();
};

class line:public point
{
protected:
double x2,y2;
public:
line(double x,double y ,double m,double n):point(x,y)
{
x2 = m;
y2 = n;
}
~line()
{}
double caldistance(double x2,double x1,double y2,double y1);
void display();
};

void point::display()
{
cout<<"输入的点的坐标为：("<}

double line::caldistance(double x2,double x1,double y2,double y1)
{
return sqrt((x2-x1)*(x2-x1)+(y2-y1)*(y2-y1));
}
void line::display()
{
cout<<"两点构成的直线距离为："<}

class Triangle:public line
{
protected :
double x3,y3;
public:
Triangle(double m,double n,double a,double b,double c,double):line(m,n,a,b)
{
x3 = a;
y3 = b;
}
~Triangle()
{}

double GetPerimeter()
{
return caldistance(x2,x1,y2,y1) + caldistance(x3,x1,y3,y1) + caldistance(x3,x2,y3,y2);
}
//求面积的算法自己做吧，我在这就不做了
//.......可以用“海伦公式”求面积，比较简单
//.......
void display()
{
cout <<"三角形的周长是："< }
};

int main()
{
point a(3.0,4.5),*p;
p = &a;
p->display();
line b(5,6,7,8);
p = &b;
p->display();
Triangle c(2,3,8,6,7,8);
p = &c;
p->display();
return 0;
}