8086 ALP: count vowels and display string

Method: read the string, count its vowels with CLASSIFY (AL = 1 means vowel) in the variable VCNT, then clear the screen and display the string followed by the vowel count in decimal.

.MODEL SMALL
.STACK 100H

DISPSTR MACRO MSG            ; display a '$'-terminated string
        LEA  DX,MSG
        MOV  AH,09H
        INT  21H
        ENDM

CLRSCR  MACRO                ; clear screen and home the cursor
        MOV  AX,0600H        ; scroll whole window (AL=0 -> blank it)
        MOV  BH,07H          ; normal attribute
        MOV  CX,0000H        ; upper-left corner (row 0, col 0)
        MOV  DX,184FH        ; lower-right corner (row 24, col 79)
        INT  10H
        MOV  AH,02H          ; set cursor position
        MOV  BH,00H          ; page 0
        MOV  DX,0000H        ; row 0, col 0
        INT  10H
        ENDM

.DATA
    MSG1  DB 'Enter a string: $'
    MSG2  DB 'String : $'
    MSG3  DB 'Number of vowels = $'
    VCNT  DB 0
    BUF   DB 80, ?, 80 DUP(0)   ; DOS buffered-input area (max, actual, chars)
    CRLF  DB 13,10,'$'

.CODE
MAIN PROC
    MOV  AX,@DATA
    MOV  DS,AX

    DISPSTR MSG1           ; prompt
    LEA  DX,BUF            ; read the string with DOS function 0Ah
    MOV  AH,0AH
    INT  21H

    LEA  SI,BUF+2
    MOV  CL,BUF+1
    MOV  CH,0
    JCXZ SHOW
NEXT:
    MOV  DL,[SI]
    CALL CLASSIFY          ; AL = 1 if vowel
    CMP  AL,1
    JNE  SKIP
    INC  VCNT              ; count vowel
SKIP:
    INC  SI
    LOOP NEXT
SHOW:
    MOV  BL,BUF+1
    MOV  BH,0
    MOV  BYTE PTR BUF[BX+2],'$'   ; terminate string
    CLRSCR
    DISPSTR MSG2
    LEA  DX,BUF+2
    MOV  AH,09H            ; display the string
    INT  21H
    DISPSTR CRLF
    DISPSTR MSG3
    MOV  AL,VCNT
    XOR  AH,AH
    CALL PRINT_DEC         ; display count
    MOV  AH,4CH            ; return to DOS
    INT  21H
MAIN ENDP

; ---- classify the character in DL
;      returns AL = 1 vowel, 2 consonant, 0 not a letter (DL unchanged)
CLASSIFY PROC
    MOV  AL,DL
    OR   AL,20H            ; fold to lower case (valid for letters)
    CMP  AL,'a'
    JB   NOTLET
    CMP  AL,'z'
    JA   NOTLET
    CMP  AL,'a'
    JE   VOW
    CMP  AL,'e'
    JE   VOW
    CMP  AL,'i'
    JE   VOW
    CMP  AL,'o'
    JE   VOW
    CMP  AL,'u'
    JE   VOW
    MOV  AL,2              ; consonant
    RET
VOW:MOV  AL,1              ; vowel
    RET
NOTLET:MOV AL,0            ; not a letter
    RET
CLASSIFY ENDP

; ---- print the unsigned number in AX in decimal (registers preserved)
PRINT_DEC PROC
    PUSH AX
    PUSH BX
    PUSH CX
    PUSH DX
    MOV  BX,10
    XOR  CX,CX             ; digit counter
PD1:XOR  DX,DX
    DIV  BX                ; AX = quotient, DX = remainder (digit)
    PUSH DX
    INC  CX
    OR   AX,AX
    JNZ  PD1
PD2:POP  DX                ; digits come out in correct order
    ADD  DL,30H            ; to ASCII
    MOV  AH,02H
    INT  21H
    LOOP PD2
    POP  DX
    POP  CX
    POP  BX
    POP  AX
    RET
PRINT_DEC ENDP

END MAIN

Output for education: String : education and Number of vowels = 5.