Fibonacci.cs

using System;

using number = System.Decimal;

namespace Fibonacci {
    class Program {

        // Recursion
        static number fibr(number n) {
            if (n == 0) { return 0; }
            if (n == 1) { return 1; }
            return fibr(n - 1) + fibr(n - 2);
        }

        // Tail Recursion
        static number fibtr(number n, number a, number b) {
            if (n == 0) { return a; }
            if (n == 1) { return b; }
            return fibtr(n-1, b, a+b);
        }

        // Iteration
        static number fibi(number n) {
            if (n == 0) { return 0; }
            if (n == 1) { return 1; }
            number a = 0, b = 1;
            for (var i=2; i <= n; ++i) {
                var c = a + b;
                a = b;
                b = c;
            }
            return b;
        }

        static void Main(string[] args) {
            for (var i=0; i < 100; i++) {
                Console.WriteLine($"fibtr({i}) = {fibtr(i, 0, 1)}, fibi({i}) = {fibi(i)}");
            }
        }
    }
}