Doing math in a batch file is a waste of time.
    There are no math functions. Luckily, all
    most people need to do is increment a counter
    of some sort. This can be done via string 
    comparisons -- something that batch files CAN 
    do. Here I show code which will increment a 
    three digit number each time it is called. 
    Looking at the code, you can see how easy it 
    would be to extend it to any length. The number 
    here is actually stored in the environment as 
    three separate variables E0, E1, and E2. To 
    refer to the entire number, you'd say this: 
    %E2%%E1%%E0%

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@echo off
:: Increments a three digit number
:: Works by comparing each digit
:: E2=hundreds, E1=tens, E0=ones
if [%E2%]==[] set E2=0
if [%E1%]==[] set E1=0
if [%E0%]==[] set E0=0
:E0
if %E0%==9 goto E1
if %E0%==8 set E0=9
if %E0%==7 set E0=8
if %E0%==6 set E0=7
if %E0%==5 set E0=6
if %E0%==4 set E0=5
if %E0%==3 set E0=4
if %E0%==2 set E0=3
if %E0%==1 set E0=2
if %E0%==0 set E0=1
goto DONE
:E1
set E0=0
if %E1%==9 goto E2
if %E1%==8 set E1=9
if %E1%==7 set E1=8
if %E1%==6 set E1=7
if %E1%==5 set E1=6
if %E1%==4 set E1=5
if %E1%==3 set E1=4
if %E1%==2 set E1=3
if %E1%==1 set E1=2
if %E1%==0 set E1=1
goto DONE
:E2
set E1=0
if %E2%==9 set E2=0
if %E2%==8 set E2=9
if %E2%==7 set E2=8
if %E2%==6 set E2=7
if %E2%==5 set E2=6
if %E2%==4 set E2=5
if %E2%==3 set E2=4
if %E2%==2 set E2=3
if %E2%==1 set E2=2
if %E2%==0 set E2=1
goto E0
:DONE
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    The way the code is shown above, the environment 
    will "remember" the value of the counter. This 
    means the next time you start the program (if you 
    start it in the same memory space), it will 
    continue counting where it left off. This is 
    great sometimes, but a bother others. If you 
    want it to always start counting over, just add 
    code like this to the batch file just before the 
    line that calls the addition batch file:

set E2=0
set E1=0
set E0=0
call add.bat

    Or you can start the counting at some 
    predetermined number like 127:

set E2=1
set E1=2
set E0=7
call add.bat

    Of course, as soon as you call add.bat, the count 
    will be at 128.

    But there are times when you just don't 
    want the leading zeros that the above 
    method mandates. For that, real math is 
    handy. Here is a routine that will 
    increment any number. Because it uses 
    QBASIC, it works great on NT, but will 
    only work on Win9x if you installed QBASIC.

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@echo off
if [%number%]==[] set number=-1
> ~temp.bas echo PRINT "set number="; LTRIM$(STR$(VAL(ENVIRON$("NUMBER")) + 1))
>>~temp.bas echo SYSTEM
qbasic /run ~temp.bas > ~temp.bat
call ~temp.bat
del ~temp.ba?
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    Batch does have the ability to count. Sort 
    of. The FIND command can count lines in a 
    file that contain certain strings. So here 
    I show a way to use a file "~counter.txt" 
    that gets a new "X" added to it every time. 
    I can count the lines to retrieve the value. 
    The cool thing about this method is that 
    several different programs in different 
    memory space can be using the same counter 
    file. If you just wanted to read the value 
    without incrementing it, just leave off the 
    second line (echo X >> ~counter.txt). If you 
    want to set the counter file to a value of 
    zero in your code, use a line like this:
echo.> ~counter.txt
    and if you want it set to a value of one:
echo X > ~counter.txt

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@echo off
echo X >> ~counter.txt
type ~counter.txt | find /c "X" > ~temp.txt
fc ~temp.txt nul /lb1 /n | date | find "1:" > en#er.bat
del ~temp.txt > nul
echo set number=%%5> enter.bat
call en#er.bat
del en?er.bat > nul
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