22.Рек.Ряд

#include "stdafx.h"
#include <cstdlib>
#include <iostream>

using namespace std;

double ryad(double a, double b);
int main() {
    double a = 1;
    double b = 0.5;
    cout << "Summa ryada: ";
    cout << ryad(a, b);
    system("pause");
    return 0;
}
double ryad(double a, double b) {
    double sum = 0;
    double buf = -(a*b / 2);
    a = b;
    b = buf;
    int i = 2;
    do {
        sum += buf;
        buf = -(a*b / 2);
        a = b;
        b = buf;
    } while (fabs(a) > fabs(b));
    return sum;
}