CODEWITHSUNDEEP
loopsbatch-file
aliksUK lockedking
aliksUK lockedking

Reputation: 1

Reading integer from text file, doing maths, writing the result back fails

I am trying to make a loop by creating a .txt file and removing numbers from it constantly until the variable in the .txt file is 0. This is how far I got: 

@echo off
set /p a=<Name.txt
set /a c=%a%-1
echo %c%> Name.txt
echo %a%
echo %c%
PAUSE

Inside the text file I input a number, for example 8. What it is meant to do is take that number and subtract 1 from it then it is meant to memorise it and then overwrite the text file again with a resut of 8 - 1 which is 7. So in the text file called Name.txt I would expect to see 7 but what I see is a blank line. Please help me out with this loop. I was trying to make an invisible code window which would appear and post a message out of nowhere.

Upvotes: 0

Views: 38

Answers (3)

aschipfl
aschipfl

Reputation: 34899

The actual problem is the line echo %c%> Name.txt in case %c holds a single decimal digit, because such is interpreted as redirection handle together with the > symbol. Your code should work with respect to that as long as %c% holds a number consisting of more than one digits.

To solve this problem, there are the following options:

  1. Move the redirection part to the front:

    > Name.txt echo %c%

    This is the most reliable solution.

  2. Put the redirected command in between parentheses:

    (echo %c%) > Name.txt

  3. Insert a SPACE in front of the > symbol:

    echo %c% > Name.txt

    Note that the added space becomes part of the output.

Upvotes: 0

Magoo
Magoo

Reputation: 79983

In place of

echo %c%> Name.txt

use

>Name.txt echo %c%

Numerics directly before redirectors may cause problems

Upvotes: 3

MichaelS
MichaelS

Reputation: 6032

I'm pretty confused by your code. You are storing the content of name.txt in the variable %a% (set /p a=<Name.txt). Then you are echoing %c% into your text file. How is this supposed to work? %c% is never set in your code. You are also missing the complete part where you are reducing the number by one. Further, you don't have to delete the file and create it again. Simply replace >> with > to overwrite the complete content of the file.

However, this code should do what you need:

@ECHO OFF
SETLOCAL EnableDelayedExpansion
:LOOP
SET /P a=<name.txt
SET /a a=!a!-1
ECHO !a!>name.txt
PAUSE
IF NOT !a!==0 GOTO LOOP

Upvotes: 1

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