Display reverse of input string.(SUB)

DECLARE SUB REV$(N$)
CLS
INPUT"ENTER STRING";N$
CALL REV$($)
END

SUB REV$(N$)
FOR I = LEN(N$) TO 1 STEP-1
B$ = MID$(N$,I,1)
C$= C$+B$
NEXT I
PRINT"REVERSE OF STRING";C$
END SUB