Letter or not

.model small
.stack 100h

.data
msg1 db 'Enter a Chracter: $'
msg2 db 0ah,0dh,'Upper case$'
msg3 db 0ah,0dh,'Lower case$'
msg4 db 0ah,0dh,'Not a letter$'


.code
main proc
    mov ax,@data
    mov ds,ax

    mov ah,9
    lea dx,msg1
    int 21h

    mov ah,1
    int 21h
    mov bl,al

    cmp bl,65
    jl a
    cmp bl, 122
    jg a

    cmp bl,65
    jge b



    b:
    cmp bl,90
    jg c

    mov ah,9
    lea dx,msg2
    int 21h
    jmp exit

    c:
    cmp bl,97
    jge d

    jmp a


    d:
    mov ah,9
    lea dx,msg3
    int 21h
    jmp exit

    a:
    mov ah,9
    lea dx,msg4
    int 21h

    exit:
    mov ah,4ch
    int 21h
    main endp
end main