Project Euler Problem 17

Definition:
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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.

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C# code solution:

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static long LettersOfNumber(long num, long[,]bases)
{
  long count = 0;
  long tempnum;
  if (num > 1000 num < 1)
    count = -1;
  else if (num == 1000)
    count = 11;
  else
  {
    tempnum = num % 100;
    if (tempnum < 20)
      count += bases[tempnum, 0];
    else
      count += bases[num % 10, 0] + bases[(num / 10) % 10, 1];
    if (num > 99)
      count += bases[(num / 100), 0] + 7 + ((tempnum == 0) ? 0 : 3);
  }
  return count;
}
static long LettersUntilNumber(int num)
{
  long letcount = 0;
  long[,] bas = new long[20, 2] { {0, 0}, {3, 0}, {3, 6}, {5, 6}, {4, 5}, {4, 5}, {3, 5}, {5, 7}, 
                  {5, 6}, {4, 6}, {3, 0}, {6, 0}, {6, 0}, {8, 0}, {8, 0}, {7, 0},
                  {7, 0}, {9, 0}, {8, 0}, {8, 0} };
  for (int i = 1; i <= num; i++)
    letcount += LettersOfNumber(i, bas);
  return letcount;
}
static void Main(string[]args)
{
  Console.WriteLine(LettersUntilNumber(1000));
  Console.ReadLine();
}

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