Notes to the K4 Simple Substitution Enciphering Program:
  
  Welcome to the K4 enciphering program.  This program was written by Archie W. Bullington in October
  2001.  I based it upon a program written by Mike Barlow.  Mr. Russell Atkinson kindly assisted me with
  some of the module programming.
  
  After downloading this program to your hard drive or diskette, double-click on the TV icon labeled
  SIMSUBK4 to begin the program.  If you wish to print the final screen showing your work, please have
  your printer turned on.
  
  The first screen shows the introduction to the program and the credits.
  
  The next 3 screens show the rules as given by the ACA for simple substitution ciphers submitted to The
  Cryptogram.  These rules are found in The ACA and You.  
  
  After the rules, an example is given for this type of key.  One keyword is used for the plain alphabet and the
  other keyword is used for the cipher alphabet with the two alphabets being different from each other.  
  
  You are then asked to enter your first keyword at the prompt.  You will then be asked for the second
  keyword.  You can enter them in either lowercase or uppercase letters.  Lowercase letters are automatically
  converted to uppercase.  If your keywords have repeated letters, the program will automatically eliminate
  all duplicate letters.  It adds the plain straight alphabet to the keywords and eliminates any duplicated letters
  as well.  The result is two keyed 26-letter alphabets.
  
  After entering your keywords, you will be asked to shift the plain alphabet from 1 to 25 spaces.  Any
  number greater than 25 will be ignored.  To finish with the plain alphabet shift-process, press '0' and then
  ENTER.  If any plain alphabet letter equals itself in the cipher alphabet, the program will not allow 0 to let
  you finish.  After finishing with the plain alphabet, you will be asked to do the same for the cipher alphabet. 
  Before finishing, the 2 alphabets must not have a plain letter equaling itself in the cipher alphabet.
  
  You will then be asked to enter the message that you want to encipher.  This can be done in either
  uppercase or lowercase letters.  The program automatically converts all lowercase letters to uppercase
  letters.  You may use normal punctuation except the double quotation mark.  To imitate this mark, use the
  apostrophe twice.  For example, ''.
  
  After entering your message, you will be asked to enter a crib or tip to aid in solving the cipher problem.  If
  you wish to include one, type it in at the prompt.  It will automatically be enciphered in a Caesar cipher
  using a shift of  6.  If you do not wish to include one, simply press the space bar once and then press the
  ENTER key.
  
  The final screen shows the keyword, the alphabets, the plain message, the enciphered message, the tip (if
  any0 and its enciphered equivalent (if any).  To print this screen, press SHIFT and the PRINT SCREEN
  keys simultaneously.  This should work, as this is a DOS program.
  
  PROGRAMMING NOTES:
  
  This program can be run within the Qbasic environment.  
  
  The string, PAK$, stands for "Press Any Key".  The UCASE$ function is used to convert lowercase letters
  to uppercase.  It ignores spaces and punctuation marks.  
  
  The algorithm that I used to eliminate duplicate letters was copied from a textbook on Qbasic.  This works
  great as Qbasic has no functions to accomplish this.  PowerBasic  3.5 has functions that delete repeated
  letters, but doesn't work within Qbasic.  The program continues to loop until the alphabet is exactly 26
  letters long.
  
  The shift algorithm gave me trouble in my original Pascal version.  Mr. Atkinson assisted me in getting it to
  work properly.    A check procedure is included along with the shift module.  It checks the alphabets for
  matches.  As long as a letter equals itself, it will not allow you to leave the shift process.
  
  The enciphering procedure examines the plain text message and locates each letter, space, or punctuation
  mark in the plain message, looks for it in the plain alphabet string, notes its position, and saves the
  corresponding letter, space, or punctuation mark in the cipher alphabet.  The result is the enciphered
  message.
  
  I used the "LOCATE" command in the wrap-up module to format the output in a neat manner.  
  
  If you have, any questions about any part of this, please e-mail me at archieb@nctc.com or
  archieb42164@yahoo.com.