China DOS Union

The original Chinese text contains some content about batch code issues. The relevant translation for the part about the problematic instruction is:

The problem with the instruction `set "char0=!choice:~%n%,1!"` is that the variable name here is wrong. It should be `char` instead of `choice`. Because earlier you used `set /p char=`, so the variable to be processed should be `char` not `choice`.

Suppose you have the statements correct elsewhere, but you set n=0 earlier and then don't change the value of n later, so in the statement "set "char0=!choice:~%n%,1!"", %n% is always 0, and you can only get the first character.

In fact, there is a problem with the statement "set "char0=!choice:~%n%,1!"" (is choice a typo for char?) in your code. I don't see the function of using !!; the whole code will have an error.

[ Last edited by namejm on 2006-8-23 at 23:55 ]

Originally posted by zts59 at 2006-8-23 19:36:
set char=
set /p char= enter:
:test
set n=0
set "char0=!char:~%n%,1!"
if %char0%="" goto end
set /A n="n+1"
echo %char0%
goto test
:end
pause


Want to achieve...

1. Logical error:
The line

set n=0

is after the subsequent goto test, which will reset the value of n to 0 again. Even if all other code is correct, it will fall into an infinite loop, continuously displaying the first character.
Correct solution:
Move it in front of the test label.
2. Syntax error:

if %char0%="" goto end

Correct solution:

if "char0%" == "" goto end

3. Command error:
The command to enable delayed environment variable expansion, setlocal ENABLEDELAYEDEXPANSION, is not used, resulting in the variables contained in the subsequent!! not being recognized and being treated as strings.
Correct solution:
Add setlocal ENABLEDELAYEDEXPANSION at the front.
Modify your code slightly as follows:

@echo off

setlocal ENABLEDELAYEDEXPANSION

    set n=0

    set char=

    set /p char=     enter:



:test

    set "char0=!char:~%n%,1!"

    if "%char0%" == "" goto end

    set /A n="n+1"

    echo %char0%

goto test



:end

    pause

Used to handle strings without sensitive characters, which is basically sufficient.

Thanks, you guys. There is indeed a typo,
and there is also a logical problem. Thanks for correcting.

Oh, and there's also an if "char0%" == "" goto end

When should we use quotes and when not?

Also, using the command to enable delayed environment variables, thank you again.