SoftUni_Homework_1_1&2

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace SoftUni_HomeWork_1_2
{
    class Program
    {
        const uint ARRAY_SIZE = 2;

        /// <summary>
        /// Check if a given number is a fibonacci number and returns its index in the sequence
        /// </summary>
        /// <param name="number">Number to be checked</param>
        /// <returns>-1 if the number is not part of the fibonacci sequence or the index of the number in the sequence</returns>
        static int Fibonacci(uint number)
        {
            //Uses a closed form solution for the fibonacci number calculation.
            //http://en.wikipedia.org/wiki/Fibonacci_number#Closed-form_expression
            double fi = (1 + Math.Sqrt(5)) / 2.0; //Golden ratio
            int n = (int)Math.Floor(Math.Log(number * Math.Sqrt(5) + 0.5, fi)); //Find's the index (n) of the given number in the fibonacci sequence
            int actualFibonacciNumber = (int)Math.Floor(Math.Pow(fi, n) / Math.Sqrt(5) + 0.5); //Finds the actual number corresponding to given index (n)
            if (actualFibonacciNumber == number)
            {
                return n;
            }
            else
            {
                return -1;
            }
        }

        /// <summary>
        /// This method tests if a given is Prime. Function is not optimized!
        /// </summary>
        /// <param name="number"> The number to be checked</param>
        /// <returns></returns>
        static bool PrimeCheck(uint number)
        {
            // Get the divisors smaller than the square root of the number
            uint divisors = (uint)Math.Sqrt(number);

            // Check if the number can be devided by any of the integer numbers smaller than its square root
            for (int cnt = 2; cnt <= divisors; cnt++)
            {
                if (number % cnt == 0)
                {
                    return false;
                }
            }
            return true;
        }

        static void Main(string[] args)
        {

            uint number = 1; // Use it to store the current value

            uint[] number_of_primes = new uint[] { 24, 101, 251 }; // This array stores the numbers of the primes asked in the task

            uint counter = 1; // Counter variable used to itterate in the loop

            while (counter <= number_of_primes[ARRAY_SIZE])
            {
                if (Program.PrimeCheck(++number)) // Increment the number and check if it's a prime number
                {
                    if (number_of_primes.Contains(counter)) // Output the value of the prime number if it's contained in the array
                    {
                        Console.Write(counter.ToString() + ": " + number.ToString());
                        int index = Fibonacci(number); // Check if the number is part of the fibonacci sequence
                        if (index != -1)
                        {
                            Console.Write(" is a fibonacci number with index: " + index.ToString() + '\n');
                        }
                        else
                        {
                            Console.Write('\n');
                        }
                    }
                    counter++;
                }
            }
            Console.ReadKey();
        }
    }
}