#include <iostream>
#include <cmath>

// 用函数模板求解定积分
class F1
{
public:
    double fun(double x) { return x * x; }
};
class F2
{
public:
    double fun(double x) { return x; }
};

template <typename T>
double integrate(T cf, double a, double b, int n = 10000)
{
    double result{(cf.fun(a) + cf.fun(b)) / 2};
    double h{(b - a) / n};
    for (int i{1}; i < n; i++)
        result += cf.fun(a + i * h);
    result *= h;
    return result;
}

int main()
{
    std::cout << integrate<F1>(F1{}, 0, 1) << '\n';
    std::cout << integrate<F2>(F2{}, 0, 1);
}