poj 1654 Area

#include<iostream>        //多边形面积
#include<string>
using namespace std;
struct point
{
    int x,y;
}p[1000010];
int move[10][2]={{},{-1,-1},{0,-1},{1,-1},{-1,0},{},{1,0},{-1,1},{0,1},{1,1}};
int main()
{
    int cases;
    string str;
    cin>>cases;
    while(cases--)
    {
        cin>>str;
        int n=str.size()-1;
        if(n<3)
        {
            printf("0\n");
            continue;
        }
        p[0].x=p[0].y=0;
        for(int i=0;i<n;++i)
        {
            p[i+1].x=p[i].x+move[str[i]-'0'][0];
            p[i+1].y=p[i].y+move[str[i]-'0'][1];
        }
        __int64 area=0;        //超int范围
        for(int i=0;i<n;++i)
            area+=p[i].x*p[i+1].y-p[i].y*p[i+1].x;
        area+=p[n].x*p[0].y-p[n].y*p[0].x;
        if(area<0)
            area=-area;
        if(area%2==0)        //答案要么是整数,要么是整数+0.5.不能用double存储,精度会不够.
            printf("%I64d\n",area/2);
        else
            printf("%I64d.5\n",area/2);
    }
    return 0;
}