FormatNum

@Echo off

:# FormatNum function by T3RRY ; Created: 25th July 2021
:# Purpose: Function to Format numbers up to 1485 digits long with coma's IE:
:#  10 = 10 ; 100 = 100 ; 1000 = 1,000 ; 10000 = 10,000 ; 100000 = 100,000 ; 1000000 = 1,000,000
:# -S and -0 switches accepted as third arg to prepend with whitespice or leading zero's respectively.

 Setlocal EnableExtensions
 %= Examples =%

:# 0 prefixed
 Call :FormatNum 1532151544621668007951135446231798748995413134278463598153468247 rv[1]1 -0
 Call :FormatNum 4071 rv[1]2 -0
 Call :FormatNum 20 rv[1]3 -0
 Call :FormatNum 3 rv[1]4 -0
 Set rv[1]

:# Whitespace prefixed
 Call :FormatNum 1532151544621668007951135446231798748995413134278463598153468247 rv[2]1 -S
 Call :FormatNum 4071 rv[2]2 -S
 Call :FormatNum 20 rv[2]3 -S
 Call :FormatNum 3 rv[3]4 -S
 Set rv[2]

:# No Prefix
 Call :FormatNum 1532151544621668007951135446231798748995413134278463598153468247 rv[3]1
 Call :FormatNum 4071 rv[3]2
 Call :FormatNum 20 rv[3]3
 Call :FormatNum 3 rv[3]4
 Set rv[3]

Endlocal
Goto :Eof

:FormatNum <Int> <ReturnVar> [-0|-S]
 If not defined FormatDelim Set "FormatDelim=," %= Allow default ',' delim to be overridden =%
 If /I "%~2"=="-0" Exit /b 3 %= Errorlevel 3 - arg2 incorrectly occuipied by arg3 =%
 If /I "%~2"=="-S" Exit /b 3
 If "%~2"=="" Exit /b 2      %= Errorlevel 2 - arg2 missing =%
 If "%~1"=="" Exit /b 1      %= Errorlevel 1 - all args missing =%

Setlocal EnableDelayedExpansion
 set "tmp=.%~1" %= No Leading zeros =%
 If "%~3"=="-0" set "tmp=.00%~1" %= Leading zeros =%
 If /I "%~3"=="-S" set "tmp=.  %~1" %= Leading whitespace =%

 %= Approximate Max string length as a multiple of 3 to reduce execution time =%
 For %%i in (1485 918 567 351 216 135 81 54 27 18 9)Do If "!tmp:~%%i,1!"=="" ( Set /A "Max=%%i" )

 For /l %%n in (!Max! -3 0)Do (
  For /f "Delims=" %%o in ('Set /A %%n+3')Do If not "%%n"=="0" (
   set "Size=!Size!%FormatDelim%!tmp:~-%%o,-%%n!"
  )Else  set "Size=!Size!%FormatDelim%!tmp:~-3!"
 )

 %= iterations below are required to remove all paired comas. =%
 For /l %%i in (0 1 8)Do set "Size=!Size:%FormatDelim%%FormatDelim%=%FormatDelim%!"
 %= remove excess leading chars =%
 set "Size=!Size:~1!"
 set "Size=!Size:.00%FormatDelim%=!"
 set "Size=!Size:.0%FormatDelim%=!"
 set "Size=!Size:.  %FormatDelim%=!"
 set "Size=!Size:. %FormatDelim%=!"
 set "Size=!Size:.%FormatDelim%=!"
 set "Size=!Size:.=!"
Endlocal & Set "%~2=%Size%"
Exit /B 0