Question

public static int Fibonacci(int n) This method receives an integer as a parameter and returns the index of n in the Fibonacci series. If n does not exist, the method returns -1. C#

Answer 1

using System;

public class FibonacciIndex
{
    public static int Fibonacci(int n) {
        if (n == 0)
            return 0;
        if (n == 1)
            return 1;
        int index = 2;
        int f0 = 1, f1 = 1;
        while (f1 <= n)
        {
            if (f1 == n)
            {
                return index;
            }

            int temp = f0;
            f0 = f1;
            f1 += temp;
            index++;
        }

        return -1;
    }
    
    public static void Main(string[] args)
    {
        Console.Write("Enter a positive integer: ");
        int n = Convert.ToInt32(Console.ReadLine());
        Console.WriteLine("Index of " + n + " is " + Fibonacci(n));
    }
}