Question

I have a password generator that uses the ascii table. I am trying to learn how to use the recursion with it. I know there are easy ways to make a generator but I want to learn more about recursion. I want it to choose the letters (65-90) but also choose the numbers (000 – 009)

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

class PasswordGenerator
{
    static void Main()
    {
        bool bypass = false;
        string errorMessage = "That is an Invalid Number, Please try again";
        string howManyCharacters = "How many Characters would you like the Password to be? (Press '0' to Stop)";
        string pressKeyMessage = "Press any key to continue";
        int length = 0;

        do
        {
            var passwordBuilder = new StringBuilder();
            Console.WriteLine(howManyCharacters);

            var inputIsNumber = int.TryParse(Console.ReadLine(), out length);

            if (!inputIsNumber)
            {
                Console.WriteLine(errorMessage);
                bypass = false;
            }
            else if (inputIsNumber && length != 0)
            {
                for (int i = 0; i < length; i++)
                    passwordBuilder.Append(GetRandomChar());

                Console.WriteLine();
                Console.WriteLine("Password: " + passwordBuilder.ToString());
                Console.WriteLine();
            }
            else
            {
                Console.WriteLine();
                Console.WriteLine(pressKeyMessage);
                Console.ReadLine();
                bypass = true;
            }
        }
        while (!bypass);
    }
    static Random _r = new Random();
    static char GetRandomChar()
    {
        return (char)_r.Next(65, 90); // A through Z
    }
}

Answer 1

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

class PasswordGenerator
{
    static void Main()
    {
        bool bypass = false;
        int length = 0;

        do
        {
            var passwordBuilder = new StringBuilder();
            Console.WriteLine("How many Characters would you like the Password to be? (Press '-1' to Stop)");

            /// try method is inside, replaced old try and catch
            var Input_is_Int = int.TryParse(Console.ReadLine(), out length);

            if (!Input_is_Int || length == 0)
            {
                Console.WriteLine("That is an Invalid Number, Please try again");
                Console.WriteLine();
                bypass = false;
            }
            else if (Input_is_Int && length != -1)
            {
                for (int i = 0; i < length; i++)
                    passwordBuilder.Append(GetRandomChar());
                Console.WriteLine("Password: " + passwordBuilder.ToString());
                Console.WriteLine();
            }
            else
            {
                Console.WriteLine();
                Console.WriteLine("Press any key to continue");
                Console.ReadLine();
                bypass = true;
            }
        }
        while (!bypass);
    }

    /// Union of ABCDEFGHIJKLMNOPQRSTUVWXYZ, 0123456789 and !"#$%&'()*+,-./ 
    static char[] _lookupTable = Enumerable.Range(65, 26).Union(Enumerable.Range(48, 10).Union(Enumerable.Range(33, 14))).Select(i => (char)i).ToArray();

    static Random _r = new Random();

    static char GetRandomChar()
    {
        var index = _r.Next(0, _lookupTable.Length);
        return _lookupTable[index];
    }
}