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The index page for all Programs on the site?

The DFF Play CD?

Zipped file DFF Play contains  executable version of about  75 of the 200+ programs from the site, mostly those I particularly liked or thought would be of widest interest for non-programmers.  The file is rather large, about 20mb..

Anything else?




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Not a programmer (yet)?

 That's OK -  the executable version for any puzzle or  game you find here is available for download.  Just scroll down to the bottom of most any description page and you'll find a "Download executable" link. Downloaded programs are in "zipped" format to reduce size and may require an "unzipper" program unless you are running Win XP or later.  Here's a link to a free one. 

Check  out  the Most Popular  Downloads from DFF   (updated weekly)

First time visitor?

Take a look at the Introduction page to see what this site is about

Notes for Teachers


What's New

May 11, 2015:  A viewer recently discovered a memory leak in our Big Integers unit which carried over to the Big Float unit.  UBigIntsV4 allows mathematical operations on integers whose size is only limited by available memory and UBigFloatV4 extends the extended precision feature to floating point numbers using UBigIntsForFloatV4 for the integer parts.   The Free method in both of the big integers unit released the memory specifically allocated by the program but neglected to call the inherited Free method which releases the memory taken by the system when the integer object was created.    Today's' postings include a revised library zip file, DFFLibV4_11May2015 containing the revised units.  Two test programs, BigIntsTest and BigFloatTest were modified to report allocated memory after each operation to verify the correction and to help indentify future memory release problems.

Yes J!

No L


 April 29, 2015:  Three points are placed randomly on the circumference of a circle. What is the probability that all three points lie within same semicircle?   Check out Circular Reasoning to verify your answer.





April 19, 2015:

A buddy of mine is designing a Veteran's Day monument which will consist of panels representing the Armed Forces services and aligned in such a way that the sun will cast a shadow on the memorial plaque on November 11 at 11:AM.  At his location, he thought that the sun would cast the shadow again in February when the the sun will be at the same altitude at that hour.  I took advantage of the opportunity to educate him about the  "analemma" figure 8 shape of the sun's path through the sky and assure him that the February sun at 11 AM will be about 10 degrees further East than the November path.  I updated  AstroDemo Version 2.0, our Astronomy unit test program, with an "animated" analemma. That option  helped me determine that at 11:11 AM in Lucedale, MS, the crossing point of the figure 8 occurs on February 12 as days are getting longer and August 29 on the way back down, so no problem for Jim's project!  


April 13, 2015:  Here's an interesting little puzzle that requires some human thought to solve efficiently: 

A farmer tells his son to select five watermelons to take to market. Because the watermelons are sold by weight, they must be put on a scale before the trip to town, but the son makes a small mistake and weighs them in pairs. Here are the weights he comes up with, in pounds: 20, 22, ,23, 24, 25, 26, 27, 28, 30, 31.  How much does each of the watermelons weigh?  (Source: Sit & Solve® Brainteasers (Sit & Solve® Series) 

The Weighing Watermelons program posted today implements the solving strategy.


March 15, 2015: 

Another calendar puzzle that is well suited to using the computer as a helper.

The two pieces required to solve Mind Your Ps and Qs will not only be mirror imaged (flipped about their vertical axes), but also reversed to top bottom (flipped about their horizontal axes).  Interestingly, and perhaps a clue to help solving these puzzles, these two flips are equivalent to a 180 rotation.

Rather drawing heavy outlines, the two pieces are defined on the program by assigning a color to each of the two letters and assigning colors to other grid cells by clicking.  

March 8, 2015:  Windows makes it's time zone information available to programs in a "TimeZoneInformation" record.  Several years ago I wrote a program to illustrate how to access this information in Delphi,  the namesake programming language for this site.  TimeZoneDemo Version 2 corrects the Daylight Saving time start and end date displays from that record which requires an undocumented  "trick" to display correctly.  The system "Day of Month" value in these fields does not contain day of month but rather acts as a template defining which occurrence of the "Day of Week" value defines Daylight Savings starts and ends (1st Sunday, 3rd Wednesday, etc).  The supplied values are now converted to the correct "Day of Month" in the program display.

March 3, 2015:

This puzzle type requires the player to find the word for the missing row of a 3-row grid such that every column is a valid 3-letter word.   WordGrid_3LetterWords Version  2.0 posted today reflects changes required to solve the 7 column Mensa Calendar puzzle for February 13, 2015 (shown at right).  As usual when I revisit a program, a  couple of additional  enhancements are  included.

February 18, 2015:  Several years ago I was attracted to the problem of locating objects from sensors which could measure distance to a target but had no idea about its direction.   Your GPS is an example of such a target which does the calculation by reading satellite signals containing timestamps allowing the device to calculate how far it is from each satellite.  It takes 4 such satellite signals to determine a location using mathematics similar to those contained in my program, Point from 4 Sensors.   A viewer recently reported an error in a sample sensor equation in the web page description, although the implementation in the program was correct.  In the process of verifying (and correcting) the web page error, I cleaned up a couple problems with  program displays caused by my use of text scaling on my monitor. Since I had the program open anyway, I fixed those and posted the update today as Version 5.1.

February 15, 2015:  Having survived Friday the 13th, I resurrected this Friday the 13th program  to check for other occurrences this year and discovered that we have two more (in March and November).  That's the maximum that can occur in a year and we won't see three in a year again until 2026, then 2037.   It's an interesting mental exercise to understand why there are 11 year gaps going forward but only 6 years since the last occurrence when I first posted this program in in 2009.  The program is also useful for finding  occurrences of specific days and dates, e.g. when is the next time your birthday falls on your birth day?  

 February 10:  The RSA Key algorithm is well known to those involved with securely exchanging data electronically.  I implemented my demo version because I wanted to see how it worked and "just for fun".  RSA  Public Key Demo V2.1 was posted today fixing a subtle bug which occasionally generated RSA keys so secure that the encrypted data could never be decrypted!   I had never encountered the error myself, but a sharp user did and even provided a program to replicate the error.      

February 2, 2015:  Two small updates this week.  If you already have these programs but haven't seen the problems fixed, it's probably not worth the time to download. 

Logic Problem Solver  V5.5 fixes a problem a user was having saving a new logic case.  Making the automatic backup copy of the existing file with that name failed under some conditions.           

The Unscramble V2.2, program, part of our Wordstuff collection, corrects range of maximum and minimum word lengths to find.  It now keeps them within the valid range based on the length of the current scrambled word. 

January 26, 2015:

A start at finding word for "dart-shooting" tube

Here's a "Word Search" puzzle solver motivated  by a Mensa Puzzle Calendar entry which asks viewers to find five 7-letter words in the given grid by following "crooked" paths. The search rules require moving  from each letter to an adjacent letter horizontally, vertically, or diagonally to the next letter and no letter may be revisited within a single word.  The puzzle is one of several included in the program downloads.

Users may play by clicking cells to form words.  They may also  change size, contents, target words, search style, etc.  and save/reload modified or new puzzles. 


January 18, 2015:  

Last month's update to our Brute Force program stopped automatically displaying the equations and parameters I used to solve each puzzle.  It accidentally flagged the puzzle as changed when the button to display that information was clicked.  As a result, when the puzzle was closed users were always asked if they wanted to save changes.  Brute Force Version 3.4 corrects that problem.  It also corrects a scaling problem which occurred in the "Change Title" dialogs for lower resolution screens. Finally, the program also now allows removing images associated with puzzles if no longer wanted. Formerly, they could be added or changed but not removed. 

These problems were found when I was solving yesterday's Mensa Calendar puzzle displayed at right.  It is included with the current downloads and, surprisingly, can be solved with only two equations! 

By the way,  the 2015 Mensa Puzzle Calendar is now on sale at Amazon for 1/2 price ($6.99).  If you enjoy puzzles, check it out.


The What's New Archives

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