FZUACM Problem 1120 A Pilot in Danger!

#include <iostream>
#include <cmath>
#include <algorithm>
#include <cstdio>
#include <cstring>
#include <vector>
using namespace std;
//2013-06-05 17:19:28 	Accepted 	1120 	GNU C++		0 ms 	856KB 	2352B 
const double eps = 1e-8;
int dcmp(double x) {
    if(fabs(x) < eps) return 0;
    if(x > 0) return 1;
    return -1;
}

struct point {
    double x, y;
    point() {}
    point(double a, double b) : x(a), y(b) {}
    friend point operator - (const point &a, const point &b) {
       return point(a.x-b.x, a.y-b.y);
    }
    friend point operator + (const point &a, const point &b) {
        return point(a.x+b.x, a.y+b.y);
    }
};

double det(const point &a, const point &b) {
   return a.x * b.y - a.y * b.x;
}

double dot(const point &a, const point &b) {
    return a.x*b.x + a.y*b.y;
}

bool PointOnSegment(point p, point s, point t) {
    return dcmp(det(p-s, t-s))==0 && (dcmp(dot(p-s, p-t))<=0);
}
const int maxn = 40100;
//多边形的点顺时针，逆时针都可以。
struct polygon {
    int n;
    point a[maxn];
    //polygon() {}
    int Point_In(point t) {
        int num = 0, i, d1, d2, k;
        a[n] = a[0];
        for(i = 0; i < n; i++) {
            if(PointOnSegment(t, a[i], a[i+1])) return 2;
            k = dcmp(det(a[i+1]-a[i], t-a[i]));
            d1 = dcmp(a[i].y - t.y);
            d2 = dcmp(a[i+1].y - t.y);
            if(k>0 && d1<=0 && d2>0) num++;
            if(k<0 && d2<= 0 && d1>0) num--;
        }
        if(num!=0) return 1;//在多边形内。
        return 0;
    }
};

polygon v;
int main()
{
    int n;
    int p, q;
    int num = 0;
    while(scanf("%d", &n) != EOF) {
        if(n==0) break;
        v.n = n;
        for(int i = 0; i < n; i++) {
            scanf("%lf%lf", &v.a[i].x, &v.a[i].y);
        }
        scanf("%d%d", &p, &q);
        int secret = (p-1)*(q-1)/2;
        int res = v.Point_In(point(0, 0));
        printf("Pilot %d\n",  ++num);
        if(res==1) {
            printf("The pilot is in danger!\n");
            printf("The secret number is %d.\n", secret);
        } else {
            printf("The pilot is safe.\n");
        }
        cout << endl;
    }
}