Bad luck

This is a program that simply extracts numbers from buffered input. I do not have any idea why this didn’t work. I got a zero.

input:
        mov ah, 0ah		; buffered input sys call
        lea dx, strptr		; load effective address
        int 21h			; call kernel
	
        mov ah, 02h		; write character to stdout sys call
        mov dl, 0ah		; issue carriage-return
        int 21h			; call kernel
	
        lea si, string		; set source index to start of string
        mov cl, [strlen]	; set loop counter
	
here:
        mov dl, [si]		; place current character in dl
        cmp dl, '0'		; compare if below '0'
        jb traverse
        cmp dl, '9'		; compare if above '9'
        ja traverse
	
        mov ah, 02h		; write character to stdout sys call
        int 21h			; call kernel
        cmp dl, '$'		; check end-of-string sentinel
        je exit			
	
traverse:
        inc si			; increment source index pointer
	
loop here
	
exit:
        int 20h			; terminate
	
strptr  label byte
maxlen  db 49
strlen  db ?
string  db 50 dup ('$')

It runs smoothly on my machine. Damn it.