Problem Statement

Idiomatically determine all the lowercase and uppercase letters   (of the Latin [English] alphabet)   being used currently by a computer programming language. The method should find the letters regardless of the hardware architecture that is being used (ASCII, EBCDIC, or other).

Display the set of all: that can be used (allowed) by the computer program, where   letter   is a member of the Latin (English) alphabet:     a ──► z     and     A ──► Z.

You may want to mention what hardware architecture is being used, and if applicable, the operating system.

Let's start with the solution:

INCLUDE "D2:CHARTEST.ACT" ;from the Action! Tool Kit

PROC Main()
  CHAR ARRAY lower(128),upper(128)
  CHAR c
  BYTE lowerLen,upperLen

  Put(125) PutE() ;clear screen

  lowerLen=0
  upperLen=0
  FOR c=0 TO 127
  DO
    IF IsLower(c) THEN
      lowerLen==+1
      lower(lowerLen)=c
    ELSEIF IsUpper(c) THEN
      upperLen==+1
      upper(upperLen)=c
    FI
  OD
  lower(0)=lowerLen
  upper(0)=upperLen

  PrintF("lowercase letters:%E %S%E%E",lower)
  PrintF("uppercase letters:%E %S",upper)
RETURN