F(n)=(1/√5)*{[(1+√5)/2]^n - [(1-√5)/2]^n}

Fibonacci-01.cpp

#include<iostream>
#include<string>
using namespace std;

long Fibonacci(unsigned int n)
{
    if(n == 0)
        return 0;
    else if(n == 1)
        return 1;
    else
        return Fibonacci(n-1) + Fibonacci(n-2);
}

int main()
{
    cout<<"Enter An N:"<<endl;
    unsigned int number=0;
    cin>>number;
    cout<<Fibonacci(number)<<endl;
    return 0;
}

Fibonacci-02.cpp

#include<iostream>
#include<string>
using namespace std;

long Fibonacci(unsigned int n)
{
    if(n == 0)
        return 0;
    if(n == 1)
        return 1;
    long firstItem = 0;
    long secondItem = 1;
    long fib = 0;
    unsigned int cnt = 1;
    while(cnt < n)
    {
        fib = firstItem + secondItem;
        firstItem = secondItem;
        secondItem = fib;
        ++cnt;
    }
    return fib;
}

int main()
{
    cout<<"Enter A Number:"<<endl;
    unsigned int number;
    cin>>number;
    cout<<Fibonacci(number)<<endl;
    return 0;
}