438 - The circumference of the cirlce/438.cpp

   1 #include <iostream>
   2 #include<stdio.h>
   3 #include<math.h>
   4 using namespace std;
   5 struct point{
   6   double x;
   7   double y;
   8   point(double X,double Y){
   9     x=X;
  10     y=Y;
  11   }
  12 };
  13
  14 double operator |(point &a,point &b){
  15   //return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y));
  16   return hypot(a.x-b.x, a.y-b.y);
  17 }
  18
  19 const double pi = 2*acos(0);
  20 int main(){
  21
  22
  23   double x1,x2,x3,y1,y2,y3;
  24
  25   while(cin>>x1>>y1>>x2>>y2>>x3>>y3){
  26     point p(x1,y1);
  27     point q(x2,y2);
  28     point r(x3,y3);
  29     printf("%.2f\n",fabs(pi*(q|r)*(p|q)*(p|r)/((q.x-p.x)*(r.y-p.y)-(q.y-p.y)*(r.x-p.x))));
  30   }
  31
  32   return 0;
  33 }