How to resolve the algorithm Day of the week step by step in the REXX programming language

Published on 12 May 2024 09:40 PM
#Rexx

How to resolve the algorithm Day of the week step by step in the REXX programming language

Table of Contents

Problem Statement

A company decides that whenever Xmas falls on a Sunday they will give their workers all extra paid holidays so that, together with any public holidays, workers will not have to work the following week (between the 25th of December and the first of January).

In what years between 2008 and 2121 will the 25th of December be a Sunday? Using any standard date handling libraries of your programming language; compare the dates calculated with the output of other languages to discover any anomalies in the handling of dates which may be due to, for example, overflow in types used to represent dates/times similar to   y2k   type problems.

Let's start with the solution:

Step by Step solution about How to resolve the algorithm Day of the week step by step in the REXX programming language

Source code in the rexx programming language

    do year=2008 to 2121
    if date('w', year"1225", 's') == 'Sunday'  then say year
    end   /*year*/

    do year=2008 to 2121
    if date('b', year"1225", 's') // 7 == 6  then say year
    end   /*year*/

/*REXX program displays in which  years  12/25  (December 25th)   falls on a  Sunday.   */
parse arg start finish .                         /*get the  START  and  FINISH  years.  */
if  start=='' |  start==","  then  start=2008    /*Not specified?  Then use the default.*/
if finish=='' | finish==","  then finish=2121    /* "       "        "   "   "     "    */

      do y=start  to finish                      /*process all the years specified.     */

      if date('Weekday', y"-12-25", 'ISO')\=='Sunday'  then iterate

   /* if date('w'      , y"-12-25", 'i'  ) ···       (same as above).  */
   /*          ↑↑↑↑↑↑   ↑↑↑↑↑↑↑↑↑↑  ↑↑↑                                */
   /*          option   yyyy-mm-dd  fmt                                */

      say 'December 25th,'    y    "falls on a Sunday."
      end   /*y*/
                                                 /*stick a fork in it,  we're all done. */

/*REXX program (old school) displays in which years 12/25 (Dec. 25th) falls on a Sunday.*/
parse arg start finish .                         /*get the  START  and  FINISH  years.  */
if  start=='' |  start==","  then  start=2008    /*Not specified?  Then use the default.*/
if finish=='' | finish==","  then finish=2121    /* "       "        "   "   "     "    */

      do y=start  to finish                      /*process all the years specified.     */
      if dow(12,25,y)==1  then say 'December 25th,'       y       "falls on a Sunday."
      end   /*y*/
exit                                             /*stick a fork in it,  we're all done. */
/*──────────────────────────────────────────────────────────────────────────────────────*/
dow: procedure; parse arg m,d,y;                 if m<3  then do;  m= m+12;  y= y-1;  end
     yL= left(y, 2);      yr= right(y, 2);  w= (d + (m+1)*26%10 +yr +yr%4 +yL%4 +5*yL) //7
     if w==0  then w= 7;  return w               /*Sunday=1,  Monday=2,  ···  Saturday=7*/

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