//Gauss求積法五點公式
#include <iostream>
#include <math.h>

using namespace std;

class quadrature
{
private:
 int i;
 double a, b, f, integral, sum;
 double w[5], x[5];

public:
 double func(double r)
 {
  f = 8.168 * r * pow((1 - r / 2.5), 0.17);
  return f;
 }
 void integration();
};

void main()
{
 quadrature legendre;
 legendre.integration();
}

void quadrature::integration()
{
 w[0] = 0.2369269;
 w[1] = 0.4786287;
 w[2] = 0.5688889;
 w[3] = 0.4786287;
 w[4] = 0.2369269;
 x[0] = -0.90617985;
 x[1] = -0.53846931;
 x[2] = 0.0;
 x[3] = 0.53846931;
 x[4] = 0.90617985;
 cout << "\n輸入下限和上限：";
 cin >> a >> b;
 sum = 0.0;
 for (i = 0; i < 5; i++)
 {
  sum += w[i] * func((x[i] * (b - a) + b + a) / 2);
 }
 integral = ((b - a) / 2) * sum;
 cout << endl << "積分值 = " << integral << endl;
}