E#4

#include "stdafx.h"
#include <iostream>
#define _USE_MATH_DEFINES
#include "math.h"

using namespace std;

int fact(int n) {
    switch (n) {
    case 0: return 1;
    case 1: return 1;
    default: {
        int k = 1;
        for (int i = 1; i <= n; i++)
            k *= i;
        return k;
    }
    }
}

double receq(double x, double f, double fk, double e, double xi, int i) {
    double t = -1 * xi * pow(x, 2) * ((1.0 / fact(i)) + (1.0 / fact(2 * i - 1))) / ((1.0 / fact(i - 1)) + (1.0 / fact(2 * i - 3)));
    f += t;
    if (abs(f - fk) < e) {
        return f;
    }
    else {
        return receq(x, f, fk, e, t, i + 1);
    }
}

void main()
{
    double e;
    cout << "Input accuracy of calculation" << endl;
    cin >> e;
    double x;
    cout << "Input point of equation" << endl;
    cin >> x;
    double k, t;
    k = x * sin(x) - exp(pow(x, 2) * -1) + 1;
    double r;
    double xf1 = pow(x, 2) * ((1.0 / fact(1)) + (1.0 / fact(1)));
    r = receq(x, xf1, k, e, xf1, 2);
    cout.precision(15);
    cout << "k = " << k << endl;
    cout << "r = " << r << endl;
    system("pause");
}