NumbersToWords

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

namespace NumberAsWords
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("Please enter a number (0-999):");
            int number = int.Parse(Console.ReadLine());
            if (number < 0 || number > 999)
            {
                Console.WriteLine("Invalid input!");
            }
            int firstDigit = number / 100;
            int secondDigit = number / 10 % 10;
            int thirdDigit = number % 100 % 10;
            if (number == 0)
            {
                Console.WriteLine("zero");
            }
            if (number % 100 == 0)
            {
                switch (firstDigit)
                {
                    case 1:
                        Console.Write("One hundred");
                        Console.WriteLine();
                        break;
                    case 2:
                        Console.Write("Two hundred");
                        Console.WriteLine();
                        break;
                    case 3:
                        Console.Write("Three hundred");
                        Console.WriteLine();
                        break;
                    case 4:
                        Console.Write("Four hundred");
                        Console.WriteLine();
                        break;
                    case 5:
                        Console.Write("Five hundred");
                        Console.WriteLine();
                        break;
                    case 6:
                        Console.Write("Six hundred");
                        Console.WriteLine();
                        break;
                    case 7:
                        Console.Write("Seven hundred");
                        Console.WriteLine();
                        break;
                    case 8:
                        Console.Write("Eight hundred");
                        Console.WriteLine();
                        break;
                    case 9:
                        Console.Write("Nine hundred");
                        Console.WriteLine();
                        break;
                }
            }
            else
            {
                switch (firstDigit)
                {
                    case 1:
                        Console.Write("One hundred and ");
                        break;
                    case 2:
                        Console.Write("Two hundred and ");
                        break;
                    case 3:
                        Console.Write("Three hundred and ");
                        break;
                    case 4:
                        Console.Write("Four hundred and ");
                        break;
                    case 5:
                        Console.Write("Five hundred and ");
                        break;
                    case 6:
                        Console.Write("Six hundred and ");
                        break;
                    case 7:
                        Console.Write("Seven hundred and ");
                        break;
                    case 8:
                        Console.Write("Eight hundred and ");
                        break;
                    case 9:
                        Console.Write("Nine hundred and ");
                        break;
                }
                if (secondDigit == 1)
                {
                    if (thirdDigit == 0)
                    {
                        switch (secondDigit)
                        {
                            case 1:
                                Console.WriteLine("ten");
                                Console.WriteLine();
                                break;
                        }
                    }
                    if (thirdDigit == 1)
                    {
                        switch (secondDigit)
                        {
                            case 1:
                                Console.WriteLine("eleven");
                                Console.WriteLine();
                                break;
                        }
                    }
                    if (thirdDigit == 2)
                    {
                        switch (secondDigit)
                        {
                            case 1:
                                Console.WriteLine("twelve");
                                Console.WriteLine();
                                break;
                        }
                    }
                    if (thirdDigit == 3)
                    {
                        switch (secondDigit)
                        {
                            case 1:
                                Console.WriteLine("thirteen");
                                Console.WriteLine();
                                break;
                        }
                    }
                    if (thirdDigit == 4)
                    {
                        switch (secondDigit)
                        {
                            case 1:
                                Console.WriteLine("fourteen");
                                Console.WriteLine();
                                break;
                        }
                    }
                    if (thirdDigit == 5)
                    {
                        switch (secondDigit)
                        {
                            case 1:
                                Console.WriteLine("fifteen");
                                Console.WriteLine();
                                break;
                        }
                    }
                    if (thirdDigit == 6)
                    {
                        switch (secondDigit)
                        {
                            case 1:
                                Console.WriteLine("sixteen");
                                Console.WriteLine();
                                break;
                        }
                    }
                    if (thirdDigit == 7)
                    {
                        switch (secondDigit)
                        {
                            case 1:
                                Console.WriteLine("seventeen");
                                Console.WriteLine();
                                break;
                        }
                    }
                    if (thirdDigit == 8)
                    {
                        switch (secondDigit)
                        {
                            case 1:
                                Console.WriteLine("eighteen");
                                Console.WriteLine();
                                break;
                        }
                    }
                    if (thirdDigit == 9)
                    {
                        switch (secondDigit)
                        {
                            case 1:
                                Console.WriteLine("nineteen");
                                Console.WriteLine();
                                break;
                        }
                    }
                }
                if (secondDigit != 1)
                {
                    switch (secondDigit)
                    {
                        case 2:
                            Console.Write("twenty ");
                            break;
                        case 3:
                            Console.Write("thirty ");
                            break;
                        case 4:
                            Console.Write("forty ");
                            break;
                        case 5:
                            Console.Write("fifty ");
                            break;
                        case 6:
                            Console.Write("sixty ");
                            break;
                        case 7:
                            Console.Write("seventy ");
                            break;
                        case 8:
                            Console.Write("eighty ");
                            break;
                        case 9:
                            Console.Write("ninety ");
                            break;
                        default:
                            Console.WriteLine();
                            break;
                    }
                    switch (thirdDigit)
                    {
                        case 1:
                            Console.Write("one");
                            Console.WriteLine();
                            break;
                        case 2:
                            Console.Write("two");
                            Console.WriteLine();
                            break;
                        case 3:
                            Console.Write("three");
                            Console.WriteLine();
                            break;
                        case 4:
                            Console.Write("four");
                            Console.WriteLine();
                            break;
                        case 5:
                            Console.Write("five");
                            Console.WriteLine();
                            break;
                        case 6:
                            Console.Write("six");
                            Console.WriteLine();
                            break;
                        case 7:
                            Console.Write("seven");
                            Console.WriteLine();
                            break;
                        case 8:
                            Console.Write("eight");
                            Console.WriteLine();
                            break;
                        case 9:
                            Console.Write("nine");
                            Console.WriteLine();
                            break;
                    }
                }
            }
        }
    }
}