判断点在多边形内外（角度判别法）

#include<iostream>
#include<cmath>
#define MAX 10000
#define PI 3.141592653589793
using namespace std;
typedef struct point{
   double x, y;
}point;

bool Is_inline(point Q, point Pi, point Pj){
   if((Q.x-Pi.x)*(Pj.y-Pi.y) == (Pj.x-Pi.x)*(Q.y-Pi.y)&&
      min(Pi.x,Pj.x) <= Q.x && Q.x <= max(Pi.x, Pj.x)&&
      min(Pi.y, Pj.y)<=Q.y && Q.y<=max(Pi.y, Pj.y)){
         return true;
      }
         return false;
}

bool Is_inside(point *set, int N, point p){
   int i, j;
   double angle = 0.0;
   bool inside = false;
   for(i=0,j=N-1; i<N; j=i++){
      if(set[i].x == p.x && set[i].y == p.y){
         inside = true;
         break;
      }
      else if(Is_inline(p, set[i], set[j])){
         inside = true;
         break;
      }
      double x1, y1, x2, y2;
      x1 = set[i].x - p.x;
      y1 = set[i].y - p.y;
      x2 = set[j].x - p.x;
      y2 = set[j].y - p.y;
      double radian = atan2(y1, x1) - atan2(y2, x2);
      radian = abs(radian);
      if(radian > PI){
         radian = 2*PI - radian;
      }
      angle += radian;
   }
   if(fabs(6.283185307179586 - angle < 1e-5)){
      inside = true;
   }
   return inside;
}

int main()
{
   int T, n;
   point temp[MAX], U;
   scanf("%d", &T);//几组数据
   for(int i = 0; i<T; i++){
      scanf("%d", &n);//多边形有n个顶点
      for(int j = 0; j < n; j++){
         scanf("%lf%lf", &temp[j].x, &temp[j].y);
      }
      printf("输入要判断的点:\n");
      scanf("%lf%lf", &U.x, &U.y);
      bool res = Is_inside(temp, n, U);
      memset(temp, 0, sizeof(point));
      if(res==true){
         printf("OK!\n");
         continue;
      }
      printf("Out!\n");
   }
   return 0;
}