(10-16)E

#include <iostream>

using namespace std;

//1
int f(int n)
{
    if(n <= 1) return 1;
    return f(n-1) * n;
}

//3
int SC(int n)
{
    if(n == 0) return 0;
    return SC(n / 10) + n % 10;
}

//4
int NrC(int n)
{
    if(n == 0) return 0;
    return NrC(n / 10) + 1;
}

//5
int Sa(int n)
{
    if(n < 1) return 0;
    return n * (n+1) + Sa(n-1);
}

double Sb(double n)
{
    if(n < 1) return 0;
    return (1 / n) + Sb(n-1);
}

double Sc(double n)
{
    if(n < 1) return 0;
    return n / ((n + 1)*(n + 2)) + Sc(n-1);
}

int main()
{
    cout << f(4) << "\n\n";
    cout << SC(123) << "\n\n";
    cout << NrC(1234) << "\n\n";
    cout << Sa(3) << "\n\n";
    cout << Sb(3) << "\n\n";
    cout << Sc(3) << "\n\n";
    return 0;
}