Strange behavior of batch file

Question

I have two cmd files. child.cmd:

@echo off
exit 1

parent.cmd:

@echo off
cmd /C child.cmd
if %errorlevel% EQU 0 (
   echo OK
) else (
   echo ERROR
)

If to run parent.cmd, then ERROR will be printed.

But if a little change parent.cmd, then OK will be printed:

@echo off
if "YES" EQU "YES" (
   cmd /C child.cmd
   if %errorlevel% EQU 0 (
      echo OK
   ) else (
      echo ERROR
   )
)

Why OK is printed in the second example?

Answer 1

inside a code block you need delayed expansion to access %variables% :

 @echo off &setlocal enabledelayedexpansion
 if !errorlevel! EQU 0 (

Answer 2

您还可以使用以下语法而不会延迟扩展：

if errorlevel 1 if not errorlevel 2 ( echo error )