Why did void main() return a zero?

[10oTURfi]

So... I had to see for myself that void main() doesnt return anything, so I wrote a simple batch file:
(note that return.exe is a program which does nothing but return value 1 and zero.exe is program with void main() {return;})

@ECHO OFF
CLS
start /w return
ECHO.Input file name of C++ program.
SET /P variable=File name: 
ECHO.Content of errorlevel before running program was %errorlevel%
ECHO.Starting C++ Program and waiting for it to finish...
start /w %variable%
IF ERRORLEVEL 1 GOTO code1
IF ERRORLEVEL 0 GOTO code0
GOTO end
:code0
ECHO.Program has finished successfully. (Exit code %errorlevel%)
GOTO end
:code1
ECHO.Program has failed to finish successfully. (Exit code %errorlevel%)
:end
PAUSE
CLS

This was on the screen:

Input file name of your C++ program.
File name: zero
Content of errorlevel before running program was 1
Starting C++ Program and waiting for it to finish...
Program has finished successfully. (Exit code 0)
Press any key to continue...

My question is: WHY?

[Disch]

void main() actually isn't legal in C++. A strict compiler would give you an error.

The compiler is probably just having main return 0 automatically.

[helios]

Because the system expects and needs the program to return something, the compiler can't produce a program that returns nothing. Since you wrote an (illegal) main() that returns nothing, the compiler assumes you don't care what is returned and always returns success to the system.