concatenating incrementing counter to string variable in batch file

Question

I have a script to create some files using format random_tests_0, random_tests_1 but my variable is not working when adding to the string of filename.

@echo off
SETLOCAL ENABLEDELAYEDEXPANSION
set /A num=0
for %%a in (.\gpc_cfgs\*) do ( 
    ECHO !num!
    set filename = random_tests_!num!
    ECHO !filename!
    set /A num+=1
)
OUTPUT:
0
random_tests_0
1
random_tests_0

EXPECTED OUTPUT:
0
random_tests_0
1
random_tests_1

Answer 1

When setting a variable spaces either side of the = are included in both the name and the variable. You should be able to fix that by using !filename ! although the value would still begin with a possibly unwanted space too!.

The recommended syntax is Set "VariableName=VariableValue", thus:

@Echo Off
SetLocal EnableDelayedExpansion
Set "num=0"
For %%A In ("gpc_cfgs\*") Do (
    Echo !num!
    Set "filename=random_tests_!num!"
    Echo !filename!
    Set /A num+=1
)

This should output the same number of !filenames! as you have files inside gpc_cfgs.