C# program to form the Fibonacci series using recursion

Here's a C# program that forms the Fibonacci series using recursion:

using System;

class Program
{
    static void Main()
    {
        int n = 10;

        Console.WriteLine("Fibonacci series up to " + n + ":");
        for (int i = 0; i < n; i++)
        {
            Console.WriteLine(Fibonacci(i));
        }
    }

    static int Fibonacci(int n)
    {
        // Base case: if n is 0 or 1, return n
        if (n == 0 || n == 1)
        {
            return n;
        }
        else
        {
            // Recursive case: calculate the Fibonacci number by summing up 
            // the previous two Fibonacci numbers (Fibonacci(n - 1) + Fibonacci(n - 2))
            return Fibonacci(n - 1) + Fibonacci(n - 2);
        }
    }
}

In this program, we have the Fibonacci method that takes an integer n as input and returns the n-th Fibonacci number.

We have a base case where if n is 0 or 1, we directly return n itself, as the Fibonacci sequence starts with 0 and 1.

In the recursive case, we calculate the Fibonacci number by summing up the previous two Fibonacci numbers: Fibonacci(n - 1) (the (n-1)th Fibonacci number) and Fibonacci(n - 2) (the (n-2)th Fibonacci number). We make recursive calls to Fibonacci with the values (n - 1) and (n - 2).

The recursive calls continue until we reach the base case (n equals 0 or 1), at which point the recursion stops and the Fibonacci number is calculated.

Fibonacci series up to 10:
0
1
1
2
3
5
8
13
21
34

The Fibonacci series up to 10 is calculated: 0, 1, 1, 2, 3, 5, 8, 13, 21, 34.