poj 1265 pick定理的应用，水

#include<stdio.h>
#include<string.h>
#include<math.h>
#include<stdlib.h>
struct point{
int x,y;
}p[1000];
int gcd(int a,int b)
{
if(b==0) return a;
return gcd(b,a%b);
}
int onedge(int n,point *p)//多边形边上的网格点数
{
int i,ret=0;
for(i=0;i<n;i++)
ret+=gcd(abs(p[i].x-p[(i+1)%n].x),abs(p[i].y-p[(i+1)%n].y));
return ret;
}
double getarea(point *p,int n)
{
int i;
double area=0;
for(i=0;i<n;i++) area+=p[(i+1)%n].y*(p[i].x-p[(i+2)%n].x);
return area;
}
int inside(int n,point *p)
{
double area=0;
area=getarea(p,n);
return (fabs(area)-onedge(n,p))/2+1;
}
int main()
{
int t,cases=1,i;
int n,dx,dy;
scanf("%d",&t);
while(t--)
{
scanf("%d",&n);
point a;
a.x=0;a.y=0;
p[0]=a;
for(i=1;i<=n;i++)
{
scanf("%d%d",&dx,&dy);
p[i].x=p[i-1].x+dx;
p[i].y=p[i-1].y+dy;
}
int I,E;
double area;
I=inside(n,p);
E=onedge(n,p);
area=getarea(p,n)/2;
printf("Scenario #%d:\n%d %d %.1lf\n\n",cases++,I,E,area);
}
return 0;
}