L3_T2

#include <iostream>
#include <cmath>

using namespace std;
double ForProduct(int n);
double WhileProduct(int n);
double DoProduct(int n);

int main()
{
    int n;

    while(true)
    {
        cout << "enter n: "<< endl;
        cin >> n;

        if(n > 0 ) break;
        cout << "\nIncorrect input values!";
    }

    cout << "Result with for: " << ForProduct(n) << endl
         << "Result with while: " << WhileProduct(n) << endl
         << "Result with do-while: " << DoProduct(n) << endl;

    return 0;
}
double ForProduct(int n)
{
    double sum = 0;

    for(int i = 1; i <= n; i++)
    {
        sum += 1.0 / (i * (i + 1));
    }
    return sum;
}
double WhileProduct(int n)
{
    double sum = 0;
    int i = 1;

    while(i <= n)
    {
        sum += 1.0 / (i * (i + 1));
        i++;
    }
    return sum;
}
double DoProduct(int n)
{
    double sum = 0;
    int i = 1;
    do
    {
         sum += 1.0 / (i * (i + 1));
         i++;
    }
    while(i <= n);
    return sum;
}