Test

namespace _1000DaysAfterBirth
{
    using System;
    using System.Collections.Generic;
    using System.Globalization;
    using System.Linq;
    using System.Text;
    using System.Threading.Tasks;

    public class Program
    {
        public static void Main()
        {
            string[] firstNineteenNumbers = new string[]
            {
                "Zero",
                "One",
                "Two",
                "Three",
                "Four",
                "Five",
                "Six",
                "Seven",
                "Eight",
                "Nine",
                "Ten",
                "Eleven",
                "Twelve",
                "Thirteen",
                "Fourteen",
                "Fifteen",
                "Sixteen",
                "Seventeen",
                "Eighteen",
                "Nineteen"
            };

            string[] tens = new string[]
            {
                "Twenty ",
                "Thirty ",
                "Forty ",
                "Fifty ",
                "Sixty ",
                "Seventy ",
                "Eighty ",
                "Ninety "
            };

            StringBuilder test = new StringBuilder();
            for (int numberInput = 0; numberInput <= 100; numberInput++)
            {
                string result = string.Empty;
                if (numberInput >= 0 && numberInput <= 19)
                {
                    result = firstNineteenNumbers[numberInput];
                }
                else if (numberInput >= 20 && numberInput < 100)
                {
                    string secondNumber = numberInput % 10 == 0 ? string.Empty : firstNineteenNumbers[numberInput % 10];

                    result = (tens[numberInput / 10 - 2] + secondNumber);
                }
                else if (numberInput == 100)
                {
                    result = "one hundred";
                }

                test.AppendLine(result);
            }

            Console.Write(test);
        }
    }
}