Data structures and algorithms-string Fibonacci to find the nth item

Title: Define the Fibonacci sequence as follows:
/0 N=0
F (n) = 1 n=1
\ f (n-1) +f (n-2) n=2
Enter N to find the nth item of the sequence in the quickest way.

#include <stdio.h>//recursion int Fibonacci (int n) {    switch (n)    {case    0:        return 0;    Case 1:        return 1;    Default:        return Fibonacci (n-1) + Fibonacci (n-2);    }} Non-recursive int nonrecursionfibonacci (int n) {    int a = 0, b = 1;    int i;    Switch (n)    {case    0:        return 0;    Case 1:        return 1;    Default:        {for            (i = 0; i < n-1; i++)            {                int c = a + B;                A = b;                b = C;            }            return b;}}    } int main () {    int f = Fibonacci (4);    int ff = Nonrecursionfibonacci (4);    printf ("%d,%d", f,ff);    return 0;}

Data structures and algorithms-string Fibonacci to find the nth item