This task is about arrays.

For hashes or associative arrays, please see Creating an Associative Array.

For a definition and in-depth discussion of what an array is, see Array.



Task

Show basic array syntax in your language.

Basically, create an array, assign a value to it, and retrieve an element   (if available, show both fixed-length arrays and
dynamic arrays, pushing a value into it).

Please discuss at Village Pump:   Arrays.

Please merge code in from these obsolete tasks:

   Creating an Array
   Assigning Values to an Array
   Retrieving an Element of an Array


Related tasks

   Collections
   Creating an Associative Array
   Two-dimensional array (runtime)


 
===========[
ARRAY DATA STRUCTURE
 
AUTHOR: Keith Stellyes
WRITTEN: June 2016
 
This is a zero-based indexing array data structure, it assumes the following 
precondition:
 
>INDEX<|NULL|VALUE|NULL|VALUE|NULL|VALUE|NULL
 
(Where >< mark pointer position, and | separates addresses)
 
It relies heavily on [>] and [<] both of which are idioms for
finding the next left/right null
 
HOW INDEXING WORKS:
It runs a loop _index_ number of times, setting that many nulls
to a positive, so it can be skipped by the mentioned idioms. 
Basically, it places that many "milestones".
 
EXAMPLE:
If we seek index 2, and our array is {1 , 2 , 3 , 4 , 5}
 
FINDING INDEX 2:
   (loop to find next null, set to positive, as a milestone
   decrement index)
 
index
  2  |0|1|0|2|0|3|0|4|0|5|0
  1  |0|1|1|2|0|3|0|4|0|5|0
  0  |0|1|1|2|1|3|0|4|0|5|0
 
===========]
 
=======UNIT TEST=======
 SET ARRAY {48 49 50}
>>++++++++++++++++++++++++++++++++++++++++++++++++>>
+++++++++++++++++++++++++++++++++++++++++++++++++>>
++++++++++++++++++++++++++++++++++++++++++++++++++
<<<<<<++ Move back to index and set it to 2
=======================
 
===RETRIEVE ELEMENT AT INDEX===
 
=ACCESS INDEX=
[>>[>]+[<]<-] loop that sets a null to a positive for each iteration
              First it moves the pointer from index to first value
               Then it uses a simple loop that finds the next null
              it sets the null to a positive (1 in this case)
               Then it uses that same loop reversed to find the first
                 null which will always be one right of our index
                 so we decrement our index
               Finally we decrement pointer from the null byte to our
              index and decrement it
 
>>            Move pointer to the first value otherwise we can't loop
 
[>]<          This will find the next right null which will always be right
              of the desired value; then go one left
 
 
.             Output the value (In the unit test this print "2"
 
[<[-]<]       Reset array
 
===ASSIGN VALUE AT INDEX===
 
STILL NEED TO ADJUST UNIT TESTS
 
NEWVALUE|>INDEX<|NULL|VALUE etc
 
[>>[>]+[<]<-] Like above logic except it empties the value and doesn't reset
>>[>]<[-] 
 
[<]<          Move pointer to desired value note that where the index was stored
              is null because of the above loop
 
[->>[>]+[<]<] If NEWVALUE is GREATER than 0 then decrement it & then find the 
              newly emptied cell and increment it
 
[>>[>]<+[<]<<-] Move pointer to first value find right null move pointer left 
                then increment where we want our NEWVALUE to be stored then 
                return back by finding leftmost null then decrementing pointer 
                twice then decrement our NEWVALUE cell
 