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HP Forum Archive 19

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HP 35s Day of the week program
Message #1 Posted by Pablo P (Spain) on 23 June 2010, 4:38 p.m.

Hi all, I was watching a tv show about an extraordinary man who calculates mentally the day of the week of any date. Then I wrote this program for the HP 35s that uses one of that algorithms.

DAY OF THE WEEK FOR HP 35s (FROM 1901 TO 2099)

Table of Contents
=================
1 Using the program 
2 Program listing 
3 Registers 
4 Revision 

1 Using the program 
~~~~~~~~~~~~~~~~~~~~

  First execute the program: XEQ W ENTER.
  Insert the day and press R/S.
  Insert the month and press R/S.
  Insert the year (from 1901 to 2099) and press R/S.

  Then it will show a number that corresponds to the
  day of the week according to this table:

    Day         Number  
   -----------+--------
    Sunday           0  
    Monday           1  
    Tuesday          2  
    Wednesday        3  
    Thursday         4  
    Friday           5  
    Saturday         6  

2 Program listing 
~~~~~~~~~~~~~~~~~~

  Line   Instruction        
 ------+--------------------
  W001   LBL W              
  W002   INPUT D            
  W003   INPUT M            
  W004   INPUT Y            
  W005   033614625035       
  W006   1E13               
  W007   10                 
  W008   RCL M              
  W009   y^x                
  W010   ÷                  
  W011   ÷                  
  W012   FP                 
  W013   10                 
  W014   x                  
  W015   IP                 
  W016   STO N              
  W017   RCL Y              
  W018   4                  
  W019   RMDR               
  W020   x!=0? ;(not equal)  
  W021   GTO W038           
  W022   RCL Y              
  W023   100                
  W024   RMDR               
  W025   x!=0? ;(not equal)  
  W026   GTO W032           
  W027   RCL Y              
  W028   400                
  W029   RMDR               
  W030   x!=0? ;(not equal)  
  W031   GTO W038           
  W032   RCL M              
  W033   3                  
  W034   x>y?               
  W035   GTO W038           
  W036   1                  
  W037   STO+ N             
  W038   RCL Y              
  W039   1                  
  W040   -                  
  W041   ENTER              
  W042   ENTER              
  W043   ENTER              
  W044   100                
  W045   INT÷               
  W046   1                  
  W047   +                  
  W048   4                  
  W049   INT÷               
  W050   -3                 
  W051   x                  
  W052   x<>y               
  W053   4                  
  W054   INT÷               
  W055   +                  
  W056   +                  
  W057   RCL N              
  W058   +                  
  W059   RCL D              
  W060   +                  
  W061   7                  
  W062   RMDR               
  W063   STO W              
  W064   VIEW W             
  W065   RTN                

  234 Bytes

3 Registers 
~~~~~~~~~~~~

  Register   Use               Notes           
 ----------+-----------------+----------------
  D          Day of month                      
  M          Month                             
  Y          Year                              
  N          Modulus           Internal usage  
  W          Day of the week                   
  

4 Revision 
~~~~~~~~~~~

  06/23/10 - Initial release

Edited: 23 June 2010, 5:29 p.m. after one or more responses were posted

      
Re: HP 35s Day of the week program
Message #2 Posted by Pablo P (Spain) on 23 June 2010, 5:18 p.m.,
in response to message #1 by Pablo P (Spain)

Sorry, there is a problem with leap years. I will fix it.

      
Re: HP 35s Day of the week program
Message #3 Posted by Pablo P (Spain) on 23 June 2010, 5:31 p.m.,
in response to message #1 by Pablo P (Spain)

Fixed.

      
Re: HP 35s Day of the week program
Message #4 Posted by Jeff O. on 24 June 2010, 4:30 p.m.,
in response to message #1 by Pablo P (Spain)

Hello Pablo,
Thanks for the program. I think I saw the show about the man who could tell the day of the week for any given date. There was a discussion here a while back about a method to determine on which day of the week the last of February, 7 March, 4 April, 9 May, 6 June, 11 July, 8 August, 5 September, 10 October, 7 November and 12 December will fall in a given year. From there you can quickly figure what day of week any other date will fall. It was called the "doomsday" method, but I preferred to think of it as the "magic day", so that's what I called the program I wrote to calculate it. The meat of the program is the equation below, which was found at the links in message 8 of the discussion.

RMDR((2+REGX+IP(REGX/4)-IP(REGX/100)+IP(REGX/400),7)

The year you are interested in must be in stack register x.

.

Edited: 25 June 2010, 1:17 p.m.

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