Euclid(几何)

http://acm.sdut.edu.cn/sdutoj/problem.php?action=showproblem&problemid=2831

题意：已知A,B,C,D,E,F的坐标，求G，H的坐标，并且已知三角形DEF的面积等于平行四边形的面积，点H在AC上。

 #include <stdio.h>
 #include <stdlib.h>
 #include <math.h>
 #include <iostream>
 #include <string.h>
 using namespace std;
 struct Point
 {
     double x,y;
     Point(double x=,double y=):x(x),y(y) {}
 };
 typedef Point Vector;

 Vector operator -(Point a,Point b)
 {
     return Vector(a.x-b.x,a.y-b.y);
 }
 double Cross(Vector a,Vector b)
 {
     return (a.x*b.y-a.y*b.x);
 }
 int main()
 {
     double xa,ya,xb,yb,xc,yc,xd,yd,xe,ye,xf,yf;
     while(cin>>xa>>ya>>xb>>yb>>xc>>yc>>xd>>yd>>xe>>ye>>xf>>yf)
     {
         if (xa==&&ya==&&xb==&&yb==&&xc==&&yc==&&xd==&&yd==&&xe==&&ye==&&xf==&&yf==)
             break;
         Point A(xa,ya),B(xb,yb),C(xc,yc),D(xd,yd),E(xe,ye),F(xf,yf);
         Vector DE = E-D,DF= F-D,AB=B-A,AC=C-A;
         double S1 = fabs(Cross(DE,DF))*/;
         double S2 = fabs(Cross(AC,AB));
         double k = S1/S2;
         Vector AH(k*AC.x,k*AC.y);
         Point H(AH.x+xa,AH.y+ya);
         Point G(AB.x+H.x,AB.y+H.y);
         printf("%.3f %.3f %.3f %.3f\n",G.x,G.y,H.x,H.y);
     }
     return ;
 }