Set user?

[Disruptis]

I'm a noob, partially my reason for coming here, and the fact that tutorials were too hard to read through, but I have a question.

I am trying to make a login screen in a game (completely made with MS-DOS) and I was wondering if you could use the set command and the if statement to make a conditional statement depending whether or not said variable is there.

EX.

:Loginsuccess
SET variable to userguest
goto terminal

:terminal
set /p choice= ]
if '%choice%'=='open file.txt' goto test1

:test1
if variable is userguest goto goodlogin
if variable is not userguest goto badlogin

:badlogin
echo You are not logged in!