PROJECT EULER #17

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If the numbers 1 to 5 are written out in words: one, two, three, four, five, then there are 3 + 3 + 5 + 4 + 4 = 19 letters used in total.

If all the numbers from 1 to 1000 (one thousand) inclusive were written out in words, how many letters would be used?

NOTE: Do not count spaces or hyphens. For example, 342 (three hundred and forty-two) contains 23 letters and 115 (one hundred and fifteen) contains 20 letters. The use of "and" when writing out numbers is in compliance with British usage.

using System;

namespace project_euler
{
   class Program
   {
       static void Main()
       {
           //Problem 17
           DateTime start = DateTime.Now;
           int sum = 0;
           for (int j = 1; j <= 1000; j++)
           {
               int ones,temp;
               int hundreds = Math.DivRem(j, 100, out temp);
               int tens = Math.DivRem(temp, 10, out ones);
               switch (hundreds)
               {
                   case 10://one thousand
                       sum += 11;
                       break;
                   case 6://six
                   case 2://two
                   case 1://one
                       sum += 3;
                       break;
                   case 9://nine
                   case 5://five
                   case 4://four
                       sum += 4;
                       break;
                   case 8://eight
                   case 7://seven
                   case 3://three
                       sum += 5;
                       break;
               }
               if (j>99&& j<1000)
               {
                   switch (tens + ones == 0 )
                   {
                       case true://hundred
                           sum += 7;
                           break;
                       case false://hundred and
                           sum += 10;
                           break;
                   }
               }
               switch (tens)
               {
                   case 9://ninety
                   case 8://eighty
                   case 3://thirty
                   case 2://twenty
                       sum += 6;
                       break;
                   case 4://forty
                   case 6://sixty
                   case 5://fifty
                       sum += 5;
                       break;
                   case 7://seventy
                       sum += 7;
                       break;
                   case 1:
                       switch (ones)
                       {
                           case 0://ten
                               sum += 3;
                               break;
                           case 2://twelve
                           case 1://eleven
                               sum += 6;
                               break;
                           case 9://nineteen
                           case 8://eighteen
                           case 4://fourteen
                           case 3://thirteen
                               sum += 8;
                               break;
                           case 6://sixteen
                           case 5://fifteen
                               sum += 7;
                               break;
                           case 7://seventeen
                               sum += 9;
                               break;
                       }
                       break;
               }
               if (tens != 1)
               {
                   switch (ones)
                   {
                       case 6: //six
                       case 2: //two
                       case 1: //one
                           sum += 3;
                           break;
                       case 9: //nine
                       case 5: //five
                       case 4: //four
                           sum += 4;
                           break;
                       case 8: //eight
                       case 7: //seven
                       case 3: //three
                           sum += 5;
                           break;
                   }
               }
           }
           Console.WriteLine(sum);
           TimeSpan time = DateTime.Now - start;
           Console.WriteLine("This took {0}", time);
           Console.ReadKey();
       }
   }
}