杭电1071题

#include <iostream>
using namespace std;
double return_result(double x1,double x2,double x3,double y1,double a);
int main()
{
 int case_num;
 double x1,y1;
 double x2,y2;
 double x3,y3;
 double a;
 double result1; 
 double result2;

 cin>>case_num;
 for(int i=0;i<case_num;i++)
 {
  cin>>x1>>y1
     >>x2>>y2
     >>x3>>y3;
     a = (y2-y1)/((x2-x1)*(x2-x1));
  result1 = return_result(x1,x2,x3,y1,a); 
  result2 = 1/2.0*(y2+y3)*(x3-x2);
  //确定cout的输出格式
  //表示不同e记法来写浮点数
  cout.setf (ios::fixed);
  cout.setf (ios::showpoint);
  cout.precision (2);
  cout<<(result1-result2)<<endl;
 }
 return 0;
}
double return_result(double x1,double x2,double x3,double y1,double a)
{
 double result;
 //千万注意1/3.0，不是1/3
 result = (1/3.0*a*x3*x3*x3-a*x1*x3*x3+(a*x1*x1+y1)*x3)-
  (1/3.0*a*x2*x2*x2-a*x1*x2*x2+(a*x1*x1+y1)*x2);
 return result;
}