Ps: - -感觉这道题完全就是数学题...就是求知道每个顶点的坐标，然后求这个多边形的面积...
代码：#include "stdio.h"
#include "stdlib.h"
#include "math.h"
int main(){
int x[100],y[100];
int i,k,n;
double sum;
while(~scanf("%d",&n)){
if(n==0) return 0;
for(i=0;i<n;i++){
scanf("%d%d",&x[i],&y[i]);
}
sum=0;
for(i=0;i<n;i++){
if(i!=n-1){
k=(x[i]*y[i+1])-(x[i+1]*y[i]);
sum+=((double)k/2);
//printf("%.1lf",sum);
}
else if(i==n-1){
k=(x[i]*y[0])-(x[0]*y[i]);
sum+=((double)k/2);
// printf("%.1lf",sum);
}
}
printf("%.1lf\n",fabs(sum));
}
return 0;
}