QBASIC to print only vowel from given word using SUB

DECLARE SUB DISPLAY ( N$ )
INPUT " Enter any number"; N$
CALL DISPLAY ( N$ )
END

SUB DISPLAY ( N$ )
FOR I = 1 TO LEN ( N$ )
B$ = MID $ ( N$, I, 1 )
C$ = UCASE $ ( B$ )
IF C$ = "A" OR C$ = "E" OR C$ = "I" OR C$ = "O" OR C$ = "U" THEN D$ = D$ + B$
NEXT I
PRINT "Vowel="; D$
END SUB