//这是一个头文件，
class function
{
public:
	virtual double operator() (double x) const = 0;
	virtual ~function(){}
};

class myfunction :public function
{
public:
	virtual double operator()(double x)const;
};

class integration
{
public:
	virtual double operator() (double a,double b,double eps) const = 0;
	virtual ~integration(){}
};

class trapz:public integration
{
public:
	trapz (const function &f):f(f){}
	virtual double operator()(double a, double b, double eps) const;
private:
	const function &f;
};
//头文件到此为止
//一个cpp
#include"trapzint.h"
#include<cmath>

double myfunction::operator()(double x)const
{
	double d = (log10(1.0 + x)) / (1.0 + x*x);
	return d;
}

double trapz::operator()(double a, double b, double eps)const
{
	bool done = false;
	int n = 1;
	double h = b - a;
	double tn = h*(f(a) + f(b)) / 2.0;
	double t2n;
	do {
		double sum = 0;
		for (int k = 0; k < n; k++)
		{
			double x = a + (k + 0.5)*h;
			sum += f(x);
		}

		t2n = (tn + h*sum) / 2.0;
		if (fabs(t2n - tn) < eps)
			done = true;
		else {
			tn = t2n;
			n *= 2;
			h /= 2;
		}
	} while (done);
	return t2n;
}
//到此为止
//主函数
#include"trapzint.h"
#include<iostream>
#include<iomanip>
using namespace std;
int main()
{
	myfunction f;
	trapz trapz(f);
	cout <<"trapz int:" << setprecision(100) << trapz(0.0, 2.0, 1e-7) << endl;
	return 0;
}
//这个程序主要是求积分，最后书上的答案是0.5548952（精度1e-7）
//代码运行结果0.1982271