pku2242.cpp

这是ACM 方面的资料 是PKU的 北京大学的出来的

#include "stdio.h"
#include "math.h"
#define PI 3.141592653589793
int main()
{
      double a,b,c,p,s,i,r;
      double x[3];
      double y[3];
      while(scanf("%lf",x)!=-1)
      {
            scanf("%lf%lf%lf%lf%lf",y,x+1,y+1,x+2,y+2);
            a=sqrt((x[0]-x[1])*(x[0]-x[1])+(y[0]-y[1])*(y[0]-y[1]));     
            b=sqrt((x[1]-x[2])*(x[1]-x[2])+(y[1]-y[2])*(y[1]-y[2]));     
            c=sqrt((x[2]-x[0])*(x[2]-x[0])+(y[2]-y[0])*(y[2]-y[0]));
            p=(a+b+c)/2;
            s=sqrt(p*(p-a)*(p-b)*(p-c));
            r=a*b*c/s/4.0;
            printf("%.2lf\n",2*r*PI);     
      }
      return 0;
}