Вычисление суммы ряда

#include <iostream>
#include <math.h>
using namespace std;
 
double fact(int p)
{
    int fc = 1;
    for (int i = 1;i <= p;i++)
        fc *= i;
    return fc;
}
 
 
int _tmain(int argc, _TCHAR* argv[])
{
    int n;
    double first = 0, second = 1, third = 0;
    double fourth = 0, fifth = 0, sixth, seventh;
    for (int i = 1;i < 11;i++)
        first += 1.0/(i + i*i);
    for (int i = 0;i < 6;i++)
        second *= double(i + 2)/(i + 3);
 
    cout<<"for third n: ";
    cin>>n;
    for (int k = 1;k < n;k++) {
        third += 1.0/((2*k +1)*fact(k));
    }
    
    for (int a = 1;a < 6;a++) {
        double temp = 1;
        for (int b = 3;b < 7;b++) {
            temp += fact(b)/fact(a);
        }
        fourth += (1/fact(a) + temp);
    } 
 
    for (int a = 0;a < 6;a++)
        fifth += pow(2.0,a)/fact(a+1);
        
    cout<<"first: "<<first<<endl;
    cout<<"second: "<<second<<endl;
    cout<<"third: "<<third<<endl;
    cout<<"fourth: "<<fourth<<endl;
    cout<<"fifth: "<<fifth<<endl;
    return 0;
}

#include "stdafx.h"
#include "iostream"
using namespace std;
 
int _tmain(int argc, _TCHAR* argv[])
{
    setlocale(LC_ALL, "Russian");
 
    double sum = 0;
 
    for (int i=1; i<=10; i++) 
        sum = sum + 1.0 / (i + i*i);
 
    cout << "Сумма равна " << sum << endl;
 
    system("pause");
    return 0;
}