Entry

BBCBASIC: Windows: Character: Memory: Line: Can you give simple program to read 1 line from memory?

Nov 18th, 2006 02:05
Knud van Eeden,

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--- Knud van Eeden --- 18 November 2006 - 01:21 am -------------------

BBCBASIC: Windows: Character: Memory: Line: Can you give simple 
program to read 1 line from memory?

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Idea:

You start from the beginning of the line
and you keep reading characters
until you encounter the end of line marker.

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BNF

(line) is
(zero or one begin marker)
followed by (zero or more characters)
followed by (one end marker)

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Regular expression

(line) = (begin marker)? (character)* (end marker)

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or written in shorthand

L = B? C* E

where

 L = line
 B = begin of line marker
 ? = zero or one
 C = character
 * = zero or more
 E = end of line marker

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or written as a BNF diagram

                  +----<----+
                  |         |
 L = ->-+-(B)-+->-+->-(C)->-+->-(E)->-
        |     |   |         |
        +-->--+   +---->----+

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because there is a begin marker here,
you can write this as

 L = B C* E

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or written as a diagram

              +----<----+
              |         |
 L = ->-(B)->-+->-(C)->-+->-(E)->-
              |         |
              +---->----+

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or written in pseudo code

 (B)

 WHILE NOT (E)

  (C)

 ENDWHILE

 (E)

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state diagram

'line read all characters' =

                          +---<-----------+
                          |               |
->-[goto begin of line]->-+-[read char]->-+->-[found end line]->-
                          |               |
                          +--->-----------+

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Steps: Overview:

 1. -E.g. create the following program

--- cut here: begin --------------------------------------------------

 REM --- MAIN --- REM

 PROCMemoryGetLineCharacterReadAllSimple( PAGE )
 END
 :
 :
 :

 REM --- LIBRARY --- REM
 :
 REM library: memory: get: line: character: read: all: simple 
(filenamemacro=getmeasi.bbc) [kn, ri, sa, 18-11-2006 01:32:31]
 DEF PROCMemoryGetLineCharacterReadAllSimple( minI% )
 REM e.g. PROCMemoryGetLineCharacterReadAllSimple( PAGE )
 REM e.g. END
 REM e.g. :
 REM e.g. :
 REM e.g. :
 LOCAL I%
 REM goto begin of program in memory
 I% = minI%
 REM
 REM no check for begin marker
 REM
 REM while not found end marker
 WHILE NOT ( ?I% = 13 )
   PRINT; ?I%; " "; : REM get byte
   I% = I% + 1 : REM goto next byte
 ENDWHILE
 PRINT; ?I% : REM get end marker
 ENDPROC

--- cut here: end ----------------------------------------------------

 2. -Running this program will e.g. output (print) all the characters
     (bytes) starting from a given memory position until the end of
     line marker (e.g. for a tokenized program, this is 13)
     is found

--- cut here: begin --------------------------------------------------

 22 0 0 244 32 45 45 45 32 77 65 73 78 32 45 45 45 32 82 69 77 13

--- cut here: end ----------------------------------------------------

===

Internet: see also:

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