using System;

using System.Text;          

​

public class Program

{

    public static void Main()

    {

        //FibGenerator();

         Console.Write("Enter the length of the Fibonacci Series: ");  

        int length = Convert.ToInt32(Console.ReadLine());  

         Console.Write("Recursive: ");  

        for (int i = 0; i < length; i++)  

        {  

            Console.Write("{0} ", FibonacciSeriesRecursive(i));  

        }  

         Console.Write("Iterative: ");  

         for (int i = 0; i < length; i++)  

         {  

             Console.Write("{0} ", FibonacciSeries(i));  

         }  

        Console.ReadKey();  

    }

                                        //0 1 2 3 4 5 6 7 8 9 10 11 12 13  => Iteration(Index)

    static int FibonacciSeries(int n)   //0 1 1 2 3 5 8 13 21 34 55 89 144

    {  

        int firstnumber = 0, secondnumber = 1, result = 0;  

​

        if (n == 0) return 0; //To return the first Fibonacci number   

        if (n == 1) return 1; //To return the second Fibonacci number   

​

        for (int i = 2; i <= n; i++)  //n=3

        {  

            result = firstnumber + secondnumber;  //0+1   1+1  

            firstnumber = secondnumber;  //1 

            secondnumber = result;  //2

        }  

​

        return result;  

    }  

                                                         //0 1 2 3 4 5 6 7 8 9 10 11 12 13 

     public static int FibonacciSeriesRecursive(int n)   //0 1 1 2 3 5 8 13 21 34 55 89 144

     {  

         if (n == 0) return 0; //To return the first Fibonacci number   

         if (n == 1) return 1; //To return the second Fibonacci number   

         return FibonacciSeriesRecursive(n - 1) + FibonacciSeriesRecursive(n - 2);  

     }  

    private static void  FibGenerator() //0 1 1 2 3 5 8 13 21 34 55 89 144

    {

        int generateTill=11;

        int num1=0, num2 =1,num3; //fib starts with 0 1 => so making it static and the 3rd num is addition of preceeding 2 numbers

        StringBuilder sb=new();

        sb.AppendLine($"Fib sequence till {generateTill}");

        sb.Append(num1.ToString());

        sb.Append(" ");

        sb.Append(num2.ToString());

        sb.Append(" ");

        for(var i=0;i<generateTill;i++)

        {

            num3=num1+num2;

            sb.Append(num3.ToString());

            sb.Append(" ");

            num1=num2;

            num2=num3;

        }

        Console.WriteLine(sb.ToString());

    }

}