Determining the last and the first letter to occur in alphabetical order

.model small
.code
org 100h
jmp main
    parlist label byte
    maxlen db 30
    actlen db ?
    kbdata db 30 dup(' ')
   
    intro db 'Enter string:  ','$'
    first db 'First:  ','$'
    last db 'Last:  ','$'
input:
    mov ah,0ah
    lea dx,parlist
    int  21h
    ret
printing:
    mov ah,09h
    int 21h
    ret
clr_scr:
    mov ax,0600h
    mov bh,07h
    mov cx,0000h
    mov dx,184fh
    int 10h
    ret
set_cur:
    mov ah,02h
    mov bh,00h
    int 10h
    ret

main proc near
    call clr_scr
    mov dx,0000h
    call set_cur
    lea dx,intro
    call printing
    mov dx,0305h
    call set_cur
    call input
    mov dx,0505h
    call set_cur
    mov bl,actlen
    mov bh,00h
    mov al,61h
    mov cl,7ah
    mov si,00h
    mov di,00h
    lea dx,first
    call printing
    call compare1
    mov dx,0605h
        call set_cur
    lea dx,last
    call printing
    call compare2
    main endp
    end main

compare1:
mov ch,kbdata[si]
cmp ch,cl
jb below
inc si
cmp si,bx
je print1
jmp compare1

below:
mov cl,ch
mov si,00h
jmp compare1

compare2:
mov ch,kbdata[di]
cmp ch,al
ja above
inc di
cmp di,bx
je print2
jmp compare2

above:
mov al,ch
mov di,00h
jmp compare2

print1:
mov ah,02h
mov dl,cl
int 21h
ret

print2:
mov ah,02h
mov dl,al
int 21h
ret


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