using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime;

namespace IsPrimeFP{
    class Program{
        static void Main(string[] args){
            string readLine = "";
            while (readLine != "exit"){
                Console.WriteLine("Enter a number: ");
                readLine = Console.ReadLine();
                if (int.TryParse(readLine, out int enteredNumber))
                {
                    if (!IsPrime(enteredNumber)){
                        Console.WriteLine("Number {0} is a prime number", enteredNumber);
                    }
                    else{
                        Console.WriteLine("Number {0} is not a prime number", enteredNumber);
                    }
                }
                else if (readLine == "prime")
                {
                    Console.WriteLine("Entering Infinite loop:");
                    IEnumerable<int> ep = GetPrimes();
                    IEnumerator<int> enump = ep.GetEnumerator();
                    while (true)
                    {
                        enump.MoveNext();
                        Console.WriteLine(enump.Current);
                    }
                }
                else{
                    Console.WriteLine("Not a valid number!");
                }
            }

        }

        static IEnumerable<int> GetPrimes()
        {
            int i = 2;
            while (true)
            {
                if (!IsPrime(i))
                {
                    yield return i;
                }
                i++;
            }
        }

        public static bool IsPrime(int n){
            return !Enumerable.Range(2, n-2).All(num => n % num != 0);
        }
    }
}