Your code is a little strange
do you mean GOTO @LOOP instead of @LOOP? @LOOP is defining a checkpoint in code (a label)
This code looks correct
IF BUTTON() AND #A THEN
BEEP 51
ENDIF
Get rid of 051 and make it 51, in most languages like Java, putting a 0 before the number tells the compiler that that number is in the octal number system, I don't know if that's the case for SmileBASIC though.
1そうだね プレイ済み