A#1

#include "stdafx.h"
#include <iostream>
#include <iomanip>
#define _USE_MATH_DEFINES
#include "math.h"
#include <windows.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 t, double f, double x, double e, double k, int i) {
    double t1 = t * pow(x, 2) * fact(2 * (i - 1)) / fact(2 * i);
    f += t1;
    if (abs(f - k) < e) {
        return f;
    }
    else {
        return receq(t1, f, x, e, k, i + 1);
    }
}

void main()
{
    SetConsoleCP(1251);
    SetConsoleOutputCP(1251);
    double e;
    cout << "Введите точность вычисления" << endl;
    cin >> e;
    double x;
    cout << "Введите x" << endl;
    cin >> x;
    double k, t;
    k = (exp(x) + exp(-x)) / 2.0;
    double r;
    r = receq(1, 1, x, e, k, 1);
    cout.precision(15);
    cout << "k = " << fixed << k << endl;
    cout << "r = " << fixed << r << endl;
    cout << "Абсолютная погрешность = " << fixed  << k - r << endl;
    cout << "Относительная погрешность = " << fixed  << ((k - r) / k) * 100 << "%" << endl;
    system("pause");
}