向量叉乘求多变形面积

CODE

#include <iostream>

#include <algorithm>

#include <vector>

#include <fstream>

#include <cmath>

using namespace std;

struct Point 
{ 

double x, y;

};

double cross(const Point &A, const Point &B, const Point &C) 
{

    return (B.x - A.x) * (C.y - A.y) - (B.y - A.y) * (C.x - A.x);

}

double polygon_area(vector<Point>& v)

{

    double area=0;

    auto it=v.begin();

    for(;it<v.end();++it)

    {

        area+=cross({0,0},*it,*(it+1));

    }

    return abs(area/2);

}

int main()

{

    fstream fs("C:\\Documents and Settings\\Administrator\\桌面\\poly.txt");

    Point tmp;

    vector<Point> v;

    while(!fs.eof())

    {

        fs>>tmp.x>>tmp.y;

        v.push_back(tmp);

    }

    double area=polygon_area(v);

    cout<<"多边形面积为："<<area<<endl;

    return 0;

}