From QB64 Wiki
$ELSE is precompiler command, which determines which sections of code inside its blocks are included into our code for compiling.
- $IF variable = expression THEN...
- $END IF
- $ELSE must follow a valid $IF statement
- There can only be one $ELSE in an $IF-$ELSEIF-$ELSE-$END IF block, and it must be the last block selection before the $END IF. $ELSEIF can not follow $ELSE.
For the above, the CONST slash is defined by the automatic internal flag (WIN), which tells us what operating system we're using. On a windows PC, the Slash will be the backslash; for any other OS it will be the forward slash.