uva 1342（几何）

本来打算暂时不再练几何的，但是有道题看了有思路，打算写了，没想到想的那么多不对的地方，写了两个半小时，写哭了

#include <iostream>
#include <cstring>
#include <cstdio>
#include <algorithm>
#include <cmath>
using namespace std;
struct Point
{
    double x,y;
    Point(double a=0,double b=0):x(a),y(b) {}
};
typedef Point Vector;
Vector operator + (Vector A,Vector B) {return Vector(A.x+B.x,A.y+B.y); }
Vector operator - (Point A,Point B) {return Vector(A.x-B.x,A.y-B.y); }
Vector operator * (Vector A,double p) { return Vector(A.x*p,A.y*p); }
Vector operator / (Vector A,double p) { return Vector(A.x/p,A.y/p); }
const double eps = 1e-10;
int dcmp(double x)
{
    if(fabs(x)<eps) return 0;
    else return x < 0 ? -1 : 1;
}
bool operator == (const Point &a,const Point &b)
{
    return dcmp(a.x-b.x)==0&&dcmp(a.y-b.y)==0;
}
bool operator < (const Point &a,const Point &b)
{
    return a.x<b.x||(a.x==b.x&&a.y<b.y);
}
double Dot(Vector A,Vector B)  { return A.x*B.x+A.y*B.y; }
double Length(Vector A) { return sqrt(Dot(A,A)); }
double Angle(Vector A,Vector B) { return acos(Dot(A,B)/Length(A)/Length(B)); }
double Cross(Vector A,Vector B) { return A.x*B.y-A.y*B.x; }
Vector GetLineIntresectoin(Point P,Vector v,Point Q,Vector w)
{
    Vector u=P-Q;
    double t=Cross(w,u)/Cross(v,w);
    return P+v*t;
}
bool spIntersectoin(Point a1,Point a2,Point b1,Point b2)
{
    double c1=Cross(a2-a1,b1-a1), c2=Cross(a2-a1,b2-a1),
           c3=Cross(b2-b1,a1-b1), c4=Cross(b2-b1,a2-b1);
    return dcmp(c1)*dcmp(c2)<0 && dcmp(c3)*dcmp(c4)<0;
}
bool onst(Point p,Point a1,Point a2)
{
    return dcmp(Cross(a1-p,a2-p))==0&&dcmp(Dot(a1-p,a2-p))<0;
}
const int maxn=300+100;
Point p[maxn],v[maxn*maxn];
int n;
int main()
{   int cc=0;
    while(~scanf("%d",&n)&&n)
    { cc++;
         for(int i=0;i<n;i++)
         {
              scanf("%lf%lf",&p[i].x,&p[i].y);
              v[i]=p[i];
         }
         n--;
         int cnt=n;
         int e=n;
         for(int i=0;i<n;i++)
            for(int j=i+1;j<n;j++)
           if(spIntersectoin(p[i],p[i+1],p[j],p[j+1]))
           {
               v[cnt++]=GetLineIntresectoin(p[i],p[i+1]-p[i],p[j],p[j+1]-p[j]);
           }
           sort(v,v+cnt);
           cnt=unique(v,v+cnt)-v;
        for(int i=0;i<cnt;i++)
          for(int j=0;j<n;j++)
           if(onst(v[i],p[j],p[j+1])) e++;//如果一个点可以把一条边分成两部分，那么边数加一
         printf("Case %d: There are %d pieces.\n",cc,e+2-cnt);
    }
    return 0;
}