FRI13.BAS
December 1998 by Marc Kummel aka Treebeard.
Contact mkummel@rain.org, http://www.rain.org/~mkummel/

 What is FRI13?
---------------
FRI13 is a small program I wrote to explore the distribution of
Friday the 13ths over the years so that I could answer a stumper
on my Stumper Page at <http://www.rain.org/~mkummel/stumpers/>:

   Friday the 13th
   November 13, 1998

   Today is Friday the 13th!  Why is this particular day considered 
   unlucky, and just how uncommon is it?  Are there years with no 
   Friday on the 13th?  Can there be two in a row in successive 
   months?  What's the most there can be in a single year?

Using this program, you will find that every year has at least one Friday 
the 13th and at most three.  You will also find that the 13th of the month 
is *more likely* to fall on a Friday than any other day of the week over 
any 400 year period after 1752, when the Gregorian Calendar was established
in the US.  Read the FRIDAY13.TXT file for the details, then play with the 
program.


 Using FRI13:
-------------
FRI13 is a simple DOS program.  Run it in DOS, or a DOS session in Windows.
You will be asked for a starting year and how many years to count.  If you
enter a filename, you can save the results as a text file to study or print.


 The Files:
-----------
I wrote this program to solve a stumper. You'll have to study the source 
code for more inffo.  I wrote FRI13 using MS Basic PDS v7.10, but it runs 
fine in QBasic or Quick Basic.

  FRI13.EXE          DOS executable
  FRI13.BAS          BASIC source code
  FRIDAY13.TXT       Why the 13th is most likely to fall on a Friday
  README.TXT         This file
  TBVAULT.TXT        Treebeard's Basic Vault info


 Conditions:
------------
This program and source code are yours to use and modify as you will, but 
they are offered as freeware with no warranty whatsoever.  Give me credit, 
but do not distribute any changes under my name, or attribute such changes 
to me in any way.  You're on your own!  

If you find this program or code useful, then let me know what you do with 
it, as a courtesy to a fellow programmer who still hacks for fun and glory.
Any suggestions or comments will be much appreciated.

Send comments and fixes to:

  Marc Kummel aka Treebeard
  mkummel@rain.org
  http://www.rain.org/~mkummel/
  http://www.treebeard.org/

For more interesting Basic software with source code, check out Treebeard's 
Basic Vault at <http://www.rain.org/~mkummel/basic/>