/* Faan Tone Liu
   January 29, 2003
   Demo program for comp 1672
   Calculates Fibonacci numbers using a recursive algorithm
 */

#include <iostream>
using namespace std;

// prototype for our recursive function that calculates fibonacci numbers.
// Returns the value of the nth fibonacci number
int fib(int n);

int main()
{
    int n;
    cout << "This program calculates a fibonacci number for you." << endl;
    cout << "What element of the fibonacci sequence do you want? ";
    cin >> n;
    cout << "Element number " << n << " of the fibonacci sequence is " <<
           fib(n) << endl;
}

// This function calculates the nth fibonacci sequence recursively
// Base case:  If n== 0, big error!  If n==1 or n==2 , answer is 1 because
//      the first two terms of the fibonacci sequence are both 1
// Recursive step:  fib(n) = fib(n-1)+fib(n-2)
int fib(int n)
{
    if (n==0) {
        cout << "Program error...Fibonacci function called with n = 1\n";
        exit(1);   // Exit with error status
    }
    if (n==1 || n ==2)
        return 1;
    return fib(n-1) + fib(n-2);
}