Conways Game of Life in cmd batch file

Just for fun I have written a Conway's Game of Life in cmd batch file.
I like writing in batch - its restrictions and limits are its appeal.

However - it is slow, very slow on a large grid. Any tips to speed it up?

I think the slowest part is the function GETNCOUNT - this gets the count of the neighbouring 'live' cells so it is called once per cell.

```
@ECHO OFF
SETLOCAL ENABLEDELAYEDEXPANSION

IF "%3"=="" GOTO HELP
SET WIDTH=%1
SET HEIGHT=%2
SET DENSITY=%3
SET LIFECYCLE=0

::::::::::::::::::::
:: Generate Grid 'A'
:: Also for safety, delete any Grid 'B' cells that might be in memory
FOR /L %%h IN (1, 1, %HEIGHT%) DO (
FOR /L %%w IN (1, 1, %WIDTH%) DO (

SET /A RAND=!RANDOM!*100/32768
SET /A RAND=!RAND!+1

IF !DENSITY! GEQ !RAND! (
SET A[%%w][%%h]=@
) ELSE (
SET "A[%%w][%%h]= "
)

SET B[%%w][%%h]=
)
)

::::::::::::::::::::::::::::::
:: TOP OF MAIN PROCESSING LOOP
::
:: Loop through all the Grid 'A' cells
:: - Count number of neighbours
:: - Check if alive or not
:: - If required assign new alive/dead status in Grid 'B'
::
:PROCESS
SET /A LIFECYCLE=%LIFECYCLE%+1

CLS
ECHO Conway's Game of Life.
CALL :DISPLAY
ECHO Current lifecycle: %LIFECYCLE%

FOR /L %%h IN (1, 1, %HEIGHT%) DO (
FOR /L %%w IN (1, 1, %WIDTH%) DO (

CALL :GETNCOUNT %%w %%h
IF "!A[%%w][%%h]!"=="@" (SET ALIVE=Y) ELSE (SET ALIVE=N)

IF "!ALIVE!"=="Y" (
IF !NCOUNT! LSS 2 (
SET "B[%%w][%%h]= "
)
IF !NCOUNT! EQU 2 (
SET B[%%w][%%h]=@
)
IF !NCOUNT! EQU 3 (
SET B[%%w][%%h]=@
)
IF !NCOUNT! GTR 3 (
SET "B[%%w][%%h]= "
)
)

IF "!ALIVE!"=="N" (
IF !NCOUNT! EQU 3 (
SET B[%%w][%

Ok so it turns out that the using CALL in a batch script is very slow. So calling a function once per cell was very expensive time-wise.

So I knew I had to move the logic from the function GETNCOUNT into the main processing loop. However the main issue I ran into here was variable expansion.

I am storing each cell value in a variable named A[x][y] e.g. A[1][1], A[1][2], A[1][3] etc. So after I had calculated the x and y value of the neighbouring cell that I wanted to check, I had to get the value of that variable somehow.

I tried all kinds of double-expansion-nested syntax, e.g. !A[!X!][!Y!]! but this just resulted in XY because the script was trying to expand variables !A[! !][! !]!.

In the end I tried a FOR loop and this worked very nicely. E.g.:

FOR /F "tokens=1,2" %%a IN ("!X! !Y!") DO (ECHO !A[%%a][%%b]!)

So what this is doing is expanding and assigning !X! and !Y! to variables local to the FOR loop %%a and %%b. Thus I can inject them into my cell variable and expand this to get the value its assigned.

So here is the 'final' code, it works much much faster than before. I am pretty satisfied with the performance now, I don't think I can get much more speed out of it.

What I would like to do next is figure out a way to exit gracefully as the only way currently is to press CTRL+C. But that's for another time...

```
@ECHO OFF
SETLOCAL ENABLEDELAYEDEXPANSION

IF "%3"=="" GOTO HELP
SET WIDTH=%1
SET HEIGHT=%2
SET DENSITY=%3
SET GENERATION=0
SET /A CELLCOUNT=%WIDTH%*%HEIGHT%
SET ALIVECOUNT=0

::::::::::::::::::::
:: Generate grid 'A'. This grid holds the cell layout for display
:: Also for safety, delete any grid 'B' cells that might be in memory
:: Grid 'B' used to store temporary cell values before they are assigned to grid 'A'
FOR /L %%h IN (1, 1, %HEIGHT%) DO (
FOR /L %%w IN (1, 1, %WIDTH%) DO (

SET /A RAND=!RANDOM!*100/32768

IF !DENSITY! GEQ !RAND! (
SET A[%%w][%%h]=@
SET /A ALIVECOUNT=!ALIVECOUNT!+1
) ELSE (
SET "A[%%w][%%h]= "
)

SET B[%%w][%%h]=
)
)

::::::::::::::::::::::::::::::
:: TOP OF MAIN PROCESSING LOOP
::
:: Display grid 'A'
:: Loop through all the Grid 'A' cells:
:: - Get values neighbouring cells
:: - Get count of alive neighbours
:: - Apply 'Game of Life' rules and store resulting value in grid 'b' cell
:: Assign grid 'b' cell values to grid 'a' cell values
:: Loop back to start process again
:PROCESS
SET /A GENERATION=%GENERATION%+1
CLS
ECHO Conway's Game of Life.
ECHO Generation: %GENERATION%
ECHO Live Cells: %ALIVECOUNT%/%CELLCOUNT%
CALL :DISPLAY

IF "%ALIVECOUNT%"=="0" (GOTO EOF)

SET ALIVECOUNT=0
SET COUNTER=0
FOR /L %%h IN (1, 1, %HEIGHT%) DO (
FOR /L %%w IN (1, 1, %WIDTH%) DO (

SET /A COUNTER=!COUNTER!+1
TITLE Calculating Cell !COUNTER!/%CELLCOUNT%

SET X=0
SET Y=0
SET NCOUNT=0

REM Find the 3 cells above this cell
IF %%h EQU 1 (SET Y=%HEIGHT%) ELSE (SET /A Y=%%h-1)
IF %%w EQU 1 (SET X=%WIDTH%) ELSE (SET /A X=%%w-1)
FOR /F "tokens=1,2" %%a IN ("!X! !Y!") DO (IF "!A[%%a][%%b]!"=="@" (SET /A NCOUNT=!NCOUNT!+1))
SET X=%%w
FOR /F "tokens=1,2" %%a IN ("!X! !Y!") DO (IF "!A[%%a][%%b]!"=="@" (SET /A NCOUNT=!NCOUNT!+1))
IF %%w EQU %WIDTH% (SET X=1) ELSE (SET /A X=%%w+1)
FOR /F "tokens=1,2" %%a IN ("!X! !Y!") DO (IF "!A[%%a][%%b]!"=="@" (SET /A NCOUNT=!NCOUNT!+1))

REM Find the 2 cells left and right of this cell
SET Y=%%h
IF %%w EQU 1 (SET X=%WIDTH%) ELSE (SET /A X=%%w-1)
FOR /F "tokens=1,2" %%a IN ("!X! !Y!") DO (IF "!A[%%a][%%b]!"=="@" (SET /A NCOUNT=!NCOUNT!+1))
IF %%w EQU %WIDTH% (SET X=1) ELSE (SET /A X=%%w+1)
FOR /F "tokens=1,2" %%a IN ("!X! !Y!") DO (IF "!A[%%a][%%b]!"=="@" (SET /A NCOUNT=!NCOUNT!+1))

REM Find the 3 cells below this cell
IF %%h EQU %HEIGHT% (SET Y=1) ELSE (SET /A Y=%%h+1)
IF %%w EQU 1 (SET X=%WIDTH%) ELSE (SET /A X=%%w-1)
FOR /F "tokens=1,2" %%a IN ("!X! !Y!") DO (IF "!A[%%a][%%b]!"=="@" (SET /A NCOUNT=!NCOUNT!+1))
SET X=%%w
FOR /F "tokens=1,2" %%a IN ("!X! !Y!") DO (IF "!A[%%a][%%b]!"=="@" (SET /A NCOUNT=!NCOUNT!+1))
IF %%w EQU %WIDTH% (SET X=1) ELSE (SET /A X=%%w+1)
FOR /F "tokens=1,2" %%a IN ("!X! !Y!") DO (IF "!A[%%a][%%b]!"=="@" (SET /A NCOUNT=!NCOUNT!+1))

REM Check if this cell is alive or not
IF "!A[%%w][%%h]!"=="@" (
SET ALIVE=Y
SET /A ALIVECOUNT=!ALIVECOUNT!+1
) ELSE (
SET ALIVE=N
)

REM Assign live status to grid 'B' based on rules
IF "!ALIVE!"=="Y" (
IF !NCOUNT! LSS 2 (
SET "B[%%w][%%h]= "
)
IF !NCOUNT! EQU 2 (
SET B[%%w][%%h]=@
)
IF !NCOUNT! EQU 3 (
SET B[%%w][%%h

StackExchange Code Review Q#156258, answer score: 4