Converting decimal 100 to 31 30 30 in Batch

I'm trying to convert a number from a text file - lets say number.txt - from decimal 100 to ASCII 31 30 30.

Is there something I can do in batch?

I tried several things I've found on SO already - but never had the right output.

Later after I have converted that - I need to add one number up after some execution. So lets say after 109 / 31 30 39 - it should be 110 31 31 30 and not 31 30 3a for example.

Can you give me a hint?

setlocal enabledelayedexpansion
for /f "tokens=*" %%a in (nummer.txt) do (
    set line=%%a
    set a=!line:~0,1!
    set line=%%a
    set b=!line:~1,1!
    set line=%%a
    set c=!line:~2,1!
    set /a mitte=3!a!3!b!3!c!
    echo 0F0900000A00143030303030303030303030303030303030!mitte!00>com3

Solution

Please see if the following `Rem`arked batch-file example helps you out.

@Echo Off
SetLocal EnableDelayedExpansion
Rem Undefine any existing variable named inputNum.
Set "inputNum="
Rem Read input number from first line of input file.
Set /P "inputNum="<"nummer.txt"
Rem Exit script if inputNum was not defined.
If Not Defined inputNum GoTo :EOF
Rem Define a number of additional iterations [number results required - 1].
Set "#=9"
Rem Define an increment size.
Set "i=5"

Rem Define a variable for total increase, [# x i].
Set /A $=#*i
Rem Undefine an existing variable named arg.
Set "arg="
Rem Begin looping for stated iterations.
For /L %%G In (0,%i%,%$%)Do (
    Set /A arg=inputNum+%%G
    Rem Call subfunction passing the input number as an argument.
    Call :Sub "!arg!"
    Rem If successful,
    If Defined mitte (
        Rem Output resultant number sequence.
        Echo !mitte!
    ) Else (
        Rem Exit if no result sequence.
        GoTo EndIt
    )
)

:EndIt
Rem Allow time to read output before ending.
Pause
EndLocal
GoTo :EOF

:Sub
Rem Undefine any existing variable named mitte.
Set "mitte="
Rem Split each character of passed argument.
For /F Delims^=^ EOL^= %%G In ('"Cmd /U/C Echo(%~1|Find /V """')Do (
    Rem prefix each digit of inputNum with 3.
    If Not Defined mitte (Set "mitte=3%%G")Else Set "mitte=!mitte!3%%G")
Rem return to next command line after previous Call
Exit /B

For testing, you should only need to ensure that your input file path is correct, (line 6). I have additionally include a facility to output a specific number of additional iterations, (line 10), with a fixed increment, (line 12). Please adjust those as necessary.

What that does if nummer.txt contains only 401, with 9 additional iterations incrementing by 5 should output:

After testing, you'll probably want to replace Echo !mitte! with (Echo 0F0900000A00143030303030303030303030303030303030!mitte!00)>COM3, (line 26)