Fibonacci series Dynamically

Code:
#include<bits/stdc++.h>
using namespace std;
//int ar[]={1,2,3,4,5},sum;
//int x;
int n;
int f(int i)
{
    //int i=1;
//cout<<i<<" "<<x<<endl;
//x+=i;

    if(i<2)
        return i;
        return f(i-1)+f(i-2);

}
int main()
{

    while(cin>>n)
    {
        for(int i=0;i<=n;i++)
        cout<<f(i)<<" "<<endl;
    }
}

Find Factorial dynamically

#include<bits/stdc++.h>
using namespace std;
//int ar[]={1,2,3,4,5},sum;
//int x;
int n;
int f(int i,int x)
{
    //int i=1;
//cout<<i<<" "<<x<<endl;
//x+=i;

    if(i==n)
        return x*i;
        return x=f(i+1,x*i);

}
int main()
{

    while(cin>>n)
    {
        cout<<f(1,1)<<endl;
    }
}

Another code:
#include<bits/stdc++.h>
using namespace std;
//int ar[]={1,2,3,4,5},sum;
//int x;
int n;
int f(int i)
{
    //int i=1;
//cout<<i<<" "<<x<<endl;
//x+=i;

    if(i==0)
        return 1;
        return i*f(i-1);

}
int main()
{

    while(cin>>n)
    {
        cout<<f(n)<<endl;
    }
}

Summation of nth Integer number Dynamically

#include<bits/stdc++.h>
using namespace std;
//int ar[]={1,2,3,4,5},sum;
//int x;
int n;
int f(int i,int x)
{
    //int i=1;
//cout<<i<<" "<<x<<endl;
//x+=i;

    if(i==n)
        return x+i;
        return x=f(i+1,x+i);

}
int main()
{

    while(cin>>n)
    {
        cout<<f(1,0)<<endl;
    }
}

Another code:
#include<bits/stdc++.h>
using namespace std;
//int ar[]={1,2,3,4,5},sum;
//int x;
int n;
int f(int i)
{
    //int i=1;
//cout<<i<<" "<<x<<endl;
//x+=i;

    if(i==0)
        return i;
        return i+f(i-1);

}
int main()
{

    while(cin>>n)
    {
        cout<<f(n)<<endl;
    }
}