Численное интегрирование

// ConsoleApplication2.cpp : Defines the entry point for the console application.
//
 
#include "stdafx.h"
#include <iostream>
 
using namespace std;
 
double f(double x);
 
double methodTrap(double a, double b, int n, double(*func)(double))
{
    double h = (b - a) / n, sum = 0;
    for (int i = 1; i < (n); i++)
    {
        sum = sum + (f(i) + f(n));
    }
    return (h / 2)*(f(a) + 2 * sum);
}
 
int main()
{
    int n;
    cout << "n=";
    cin >> n;
    double a, b;
    cout << "a=";
    cin >> a;
    cout << "b=";
    cin >> b;
 
    cout << methodTrap(a, b, n, f) << "\n";
    system("pause");
}
 
double f(double x)
{
    return 1 / (2 + x*x);
}

double h = (b - a) / n, sum = 0, xi;
    for (int i = 1; i < (n); i++)
    {
        xi = a + i*h;
        sum = sum + (f(xi) + f(n));
    }
    return (h / 2)*(f(a) + 2 * sum);

double methodTrap(double a, double b, int n, double(*func)(double))
{
    double h = (b - a) / n, sum = 0;
    for (int i = 0; i < n; i++)
    {
        sum += 0.5 * h * (f(a + i * h) + f(a + (i + 1) * h));
    }
    return sum;
}

double methodTrap(double a, double b, int n, double(*f)(double))

// ConsoleApplication2.cpp : Defines the entry point for the console application.
//
 
#include "stdafx.h"
#include <iostream>
 
using namespace std;
 
double f(double x);
int k;
 
double methodTrap(double a, double b, int n, double(*func)(double))
{
    double h = (b - a) / n, sum = 0, xi;
    for (int i = 1; i < (n); i++)
    {
        xi = a + i*h;
        sum = sum + (f(xi) + f(n));
    }
    return (h / 2)*(f(a) + 2 * sum);
}
 
int main()
{
    int n;
    cout << "n=";
    cin >> n;
    double a, b;
    cout << "a=";
    cin >> a;
    cout << "b=";
    cin >> b;
    cout << "k=";
    cin >> k;
    double eps;
    cout << "eps=";
    cin >> eps;
 
    double res1, res2;
    res1 = methodTrap(a, b, n, f);
    for (;;)
    {
        res2 = methodTrap(a, b, n * 2, f);
        if (1/3*fabs(res1 - res2) < eps)
        {
            cout << res2;
            break;
        }
        else {
            res1 = res2;
            n = 2 * n;
        }
    }
    system("pause");
}
 
double f(double x)
{
 
    return 1 / (k + x*x);
}