It's a good idea to avoid GOTO. It's almost never necessary and tends to make programs confusing or lead to bugs.
For instance, this works:
IF B$=="+" THEN D=A+C
IF B$=="-" THEN D=A-C
etc.
whereas this has a bug in it:
IF B$=="+" THEN GOTO @PLUS
IF B$=="-" THEN GOTO @MINUS
@PLUS D=A+C
@MINUS D=A-C
Notice that after D=A+C is run, it ends up running D=A-C too.
3そうだね 未プレイ