2013寒假练习 1034：丈量土地

地址：http://acm.bit.edu.cn/mod/programming/view.php?a=520

裸的多边形面积。。三角剖分思想。今次使用了从伟神那学来的运算符重载算叉积=w=

#include<iostream>#include<cmath>using namespace std;typedef struct{double x,y;void in(){scanf("%lf%lf",&x,&y);}}point;double operator ^ (point a,point b)  {return a.x*b.y-a.y*b.x;}int main(){int n,i;point t1,t2,t;while(~scanf("%d",&n)){double ans=0;t1.in(),t=t1;for(i=1;i<n;i++){t2.in();ans+=t1^t2;t1=t2;}ans+=t1^t;printf("%.2lf\n",fabs(0.5*ans));}return 0;}