Issue in Leading zero in CMD - batch-file

Question

I am made a CMD batch file to generate the barcode numbers. Batch script generate the last ninth number of barcode by doing the calculation and generate the file named "barcode.txt". The code is working fine. Only the problem is when the "fn" number "Barcode Eight Digit " start with zero then the code is not working properly.
#echo off
setlocal EnableDelayedExpansion
set /p al=Please enter Alfa two digit:
set /p fn=Please enter Barcode Eight Digit:
set /p no=Please enter number of Barode:
set /a NUMBER=%fn%
set /a to=%no%
set /a count=1
pause
:loop
if %count% GTR %to% GOTO :end
set var1=%NUMBER:~0, 1%
set var2=%NUMBER:~1, 1%
set var3=%NUMBER:~2, 1%
set var4=%NUMBER:~3, 1%
set var5=%NUMBER:~4, 1%
set var6=%NUMBER:~5, 1%
set var7=%NUMBER:~6, 1%
set var8=%NUMBER:~7, 1%
set /A B1 = %var1% * 8
set /A B2 = %var2% * 6
set /A B3 = %var3% * 4
set /A B4 = %var4% * 2
set /A B5 = %var5% * 3
set /A B6 = %var6% * 5
set /A B7 = %var7% * 9
set /A B8 = %var8% * 7
set /A B9 = %B1% + %B2% + %B3% + %B4% + %B5% + %B6% + %B7% + %B8%
set /A B10 = (%B9%) %% 11
set /A B11 = 11- %B10%
if "%B11%"=="10" (set B11=0)
if "%B11%"=="11" (set B11=5)
echo %al%%NUMBER%%B11%IN >> barcode.txt
set /a NUMBER+=1
set /a count+=1
goto loop
:end
echo end it
pause
I tried to find the solution but failed. Can please any one help me to fix the issue while number start with zero.

Answer 1

Use
set /a NUMBER=%fn% + 100000000
(1 followed by 8 0s)
Then
echo %al%%NUMBER:~1%%B11%IN >> barcode.txt

Answer 2

Thanks to suggest me. I have made the working code by just declaring set /a NUMBER=1%fn%.
#echo off
setlocal EnableDelayedExpansion
set /p al=Please enter Alfa two digit:
set /p fn=Please enter Barcode Eight Digit:
set /p no=Please enter number of Barode:
set /a NUMBER=1%fn%
set to=%no%
set count=1
pause
:loop
if %count% GTR %to% GOTO :end
set var1=%NUMBER:~1, 1%
set var2=%NUMBER:~2, 1%
set var3=%NUMBER:~3, 1%
set var4=%NUMBER:~4, 1%
set var5=%NUMBER:~5, 1%
set var6=%NUMBER:~6, 1%
set var7=%NUMBER:~7, 1%
set var8=%NUMBER:~8, 1%
set /A B1 = var1 * 8
set /A B2 = var2 * 6
set /A B3 = var3 * 4
set /A B4 = var4 * 2
set /A B5 = var5 * 3
set /A B6 = var6 * 5
set /A B7 = var7 * 9
set /A B8 = var8 * 7
set /A B9 = B1 + B2 + B3 + B4 + B5 + B6 + B7 + B8
set /A B10 = B9 %% 11
set /A B11 = 11- B10
if "%B11%"=="10" (set B11=0)
if "%B11%"=="11" (set B11=5)
echo %al%%NUMBER:~1%%B11%IN >> barcode.txt
set /a NUMBER+=1
set /a count+=1
goto loop
:end
echo end it
pause