A-M baby

Task/Filter/REXX/filter.rexx

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+/*REXX program selects all even numbers from an array  ──► a new array. */
+numeric digits 210000                  /*handle past  1m  for Fibonacci.*/
+old.=                                  /*the OLD array, all null so far.*/
+new.=                                  /*the NEW array, all null so far.*/
+  do j=-40 to 40;  old.j=fib(j);  end  /*put 81 Fibonacci numbs ==> OLD */
+news=0                                 /*numb. of elements in NEW so far*/
+
+/*══════════════════════════════════════════════════════════════════════*/
+      do k=-40  while old.k\==''       /*process the OLD array elements.*/
+      if old.k//2 \== 0 then iterate   /*if element isn't even, skip it.*/
+      news=news+1                      /*bump the number of NEW elements*/
+      new.news=old.k                   /*assign it to the NEW array.    */
+      end
+/*══════════════════════════════════════════════════════════════════════*/
+
+      do j=1  for news                 /*display all the NEW  numbers.  */
+      say 'new.'j "=" new.j
+      end
+exit                                   /*stick a fork in it, we're done.*/
+/*─────────────────────────────────────FIB subroutine (non-recursive)───*/
+fib: procedure; parse arg n; na=abs(n); if na<2 then return na /*special*/
+a=0;  b=1
+                do j=2 to na; s=a+b; a=b; b=s; end
+
+if n>0 | na//2==1  then return  s      /*if positive or odd negative... */
+                   else return -s      /*return a negative Fib number.  */