计算边不相交的简单多边形面积的方法[简单多边形][C++]

#include <iostream>
#include <cmath>

const int NUM = 6;
//多边形的各边不能相交，不然计算会出错
//面积为正可以判断多边型正面，面积为负表示多边形背面
double GetArea( POINT *pPoint, int nNum )
{
 double S = 0;
 for(int i=0; i<nNum-1; i++)
  S+=pPoint[i].x*pPoint[i+1].y-pPoint[i+1].x*pPoint[i].y;
 S += pPoint[nNum-1].x*pPoint[0].y - pPoint[0].x*pPoint[nNum-1].y;
 S /= 2.0;
 return S;
}

int main()
{
 POINT points[NUM] = {
   {0, 0},
   {3, 12},
   {5, 6},
   {8, 8},
   {10, 2},
   {4, 4}
 };
 double ss=0;
 ss = fabs(GetArea(points, NUM));
 std::cout<<ss<<std::endl;
 return 0;
}