Command prompt script to subtract variables - batch-file

Question

I know there are many arithmetic questions on here, but I have not found the specific answer to my question. I have a file with two values in it, the first always higher than the second. Today, the txt file has:
21.04
20.94
What I am trying to do is, via a batch file, subtract the second number from the first, and then insert than on a new line. Any assistance is appreciated.

Answer 1

Just incorporate powershell into the batch file.
to test from cmd:
#for /f %i in ('powershell 21.04 - 20.94') do #echo %i
So you can build a very basic calculator rather easily.
set /p "first=Enter first number: "
set /p "second=Enter Second Number: "
set /p "function=Select Function(+-/): "
powershell %first% %function% %second%
And offcourse you can use a for loop to assign the value to a variable should you want to use it elsewhere in your batch file.
#echo off
set /p "first=Enter first number: "
set /p "second=Enter Second Number: "
set /p "function=Select Function(+-/): "
for /f %%i in ('powershell %first% %function% %second%') do set "result=%%i"
echo %result%
in a batch-file you double the % in meta variables to %%i
Assuming file is called math.txt
#echo off
setlocal enabledelayedexpansion
set cnt=1
for /f "usebackq" %%i in ("d:\math.txt") do (
set var!cnt!=%%i
set /a cnt+=1
)
(powershell %var1% - %var2%)>output.txt
pause

Answer 2

This method works with numbers up to 9 total digits (and any number of decimals) as long as the input numbers have the same number of decimals:
#echo off
setlocal EnableDelayedExpansion
rem Read two numbers
( set /P "num1=" & set /P "num2=" ) < test.txt
rem Adjust *two* numbers for given decimals
set "decimals=2"
for %%i in (1 2) do (
set "num%%i=!num%%i:.=!"
for /L %%d in (1,1,%decimals%) do if "!num%%i:~0,1!" equ "0" set "num%%i=!num%%i:~1!"
)
rem Subtract second number from the first
set /A "result=num1 - num2"
rem Adjust result for given number of decimals
for /L %%d in (1,1,%decimals%) do if "!result:~%decimals%!" equ "" set "result=0!result!"
rem Output result with decimals
echo !result:~0,-%decimals%!.!result:~-%decimals%!

Answer 3

I think this works for reasonably sized numbers:
#echo off
rem read values from file specified as command line parameter
(
set /p value1=
set /p value2=
)<%1
rem split first value into whole and fractional parts
for /f "tokens=1,2 delims=." %%a in ("%value1%") do (
set beforedot1=%%a
set afterdot1=%%b
)
rem reconstruct first value as fixed point number
set afterdot1=%afterdot1%00000
set afterdot1=%afterdot1:~0,6%
set value1=%beforedot1%%afterdot1%
rem split second value into whole and fractional parts
for /f "tokens=1,2 delims=." %%a in ("%value2%") do (
set beforedot2=%%a
set afterdot2=%%b
)
rem reconstruct second value as fixed point number
set afterdot2=%afterdot2%00000
set afterdot2=%afterdot2:~0,6%
set value2=%beforedot2%%afterdot2%
rem subtract values
set /a diff=value1-value2
rem convert fixed point value back
if "%diff:~0,-6%" == "" (
set diff=0.%diff:~-6%
) else (
set diff=%diff:~0,-6%.%diff:~-6%
)
rem remove trailing zeros
:loop
if "%diff:~-1%" == "0" (
set diff=%diff:~0,-1%
goto :loop
)
echo %diff%