Assembly Language: Determine if Digit or Not

This will determine if the user's input is a digit or not and quits if "q" is pressed.

Anyway, here's the code below:

.model small org 100h .data msg1 db 13,10,13,10, "Press Key : $" msgEr db 13,10,13,10,"Is not a digit! $" msgSuc db 13,10,13,10,"Is a digit! $" .code start: mov ax, @data mov ds, ax mov dx, offset msg1 mov ah, 09h int 21h mov ah, 01h int 21h cmp al,'q' je exit cmp al, 30h ;0 (ASCII 48) jl error cmp al, 39h ;9 (ASCII 57) jg error cmp al, 30h ;0 (ASCII 48) jg suc cmp al, 39h ;9 (ASCII 57) jl suc exit: mov ah, 4ch int 21h error: lea dx,msgEr mov ah,09h int 21h jmp start suc: lea dx,msgSuc mov ah,09h int 21h jmp start end start

It's a very simple code but it come in handy as an error handler.