hdu 2036 计算几何求面积

#include<iostream>#include<cstdio>#include<string>#include<algorithm>#include<cstring>#include<vector>#include<queue>#include<map>#include<set>using namespace std;int main(){    int n,i,a[222],b[222];    double sum;    while(scanf("%d",&n)&&n)     {for(i=0;i<n;i++)scanf("%d%d",a+i,b+i);a[n]=a[0];b[n]=b[0];//形成闭合sum=0;//s=1/2*(x2-x1)*(y3-y1)-(y2*y1)*(x3-x1)//下面x1=0,x2=0以原点分割;//逆时针算出的是正面积 顺时针是负面积for(i=1;i<=n;i++)sum+=a[i-1]*b[i]-a[i]*b[i-1];         printf("%1.1f\n",sum/2);    }}