input is number or not in assambly language

;to check whether the input is a number
.model small
.stack 100h
.data
msg db "your input is a number$"
mdg db 13,10,"your input is not a number$"
.code
start:
mov ax,@data
mov ds,ax

mov ah,1
int 21h
mov bl,al

cmp bl,58
jg line0

cmp bl,48
jl line0

mov dl,bl
lea dx,msg
mov ah,9h
int 21h
jmp down


line0:
mov dl,0
lea dx,mdg
mov ah,9h
int 21h
int 21h
jmp down

down:
mov ah,4ch
int 21h

end start