hdu 2036

水题

AC代码：

#include<iostream>using namespace std;int main(){    float n,m,x,y,x1,y1,x2,y2;    while(cin>>n,n){        double sum=0.0;    cin>>x>>y;    x1=x,y1=y;    n--;    while(n--){    cin>>x2>>y2;    sum+=abs(x1*y2-x2*y1);    x1=x2,y1=y2;}    sum+=abs(x*y2-x2*y);    printf("%.1f\n",sum/2);}    return 0;}