Как работать с <vector>

#include <iostream>
#include <vector>
#include <cmath>
#include <list>
#include <algorithm>
#define eps 1e-8;
using namespace std;
 
double area_triangle (point a, point b, point c);
bool ccw (point a, point b, point c);
double dist(point a, point b);
 
class point
{
 public: 
    double x,y;
    int i;
    point(double _x, double _y) 
     {
      x=_x;
      y=_y;
     }
    point()
     {
      point(0, 0);  
     }
};
 
point first;
 
class less_of_ccw
{
 public:
    bool operator () (point a, point b)
     {
      if (a.i==first.i) return true;
      if (b.i==first.i) return false;
      if (ccw(first,a,b)) return true;
      if (ccw(first,b,a)) return false;
      return dist(first,a)>dist(first,b);
     }
};
 
int main()
{
}
 
bool ccw (point a, point b, point c)
{
 return area_triangle(a,b,c)>eps;
}
 
double area_triangle (point a, point b, point c)
{
 return 0.5*(a.x*b.y+b.x*c.y+c.x*a.y-a.y*b.x-b.y*c.x-c.y*a.x); 
}
 
double dist(point a, point b)
{
 return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y));
}
 
void hull_graham (vector <point> p, vector <int> &ip)
{
 int n=p.size();
 int i;
 for (i=0; i<n; ++i) p[i].i=i;
 first=p[0];
 for (i=1; i<n; ++i)
 if (first.x>p[i].x || (first.x==p[i].x && first.y>p[i].y)) first=p[i];
 sort (p.begin(), p.end(), less_of_ccw());
 ip.push_back (0);
 for (i=1; i<n && abs(area_triangle(p[0],p[1],p[i]))<=eps; ++i);
 ip.push_back (1);
 int top=1;
 while (i<n)
  {
   if (!ccw(p[ip[top-1]],p[ip[top]],p[i]))
    {
     --top;
     ip.pop_back ();
    }
   else
    {
     ++top;
     ip.push_back (i);
     ++i;
    }
  }
 for (i=0; i<ip.size(); ++i) ip[i]=p[ip[i]].i;
}