data segment
    kb_buffer db 100 dup(?)
    nsum db ?
data ends
code segment
     assume cs:code,ds:data
start:mov ax,code
      mov cs,ax
      mov ax,data
      mov ds,ax
      mov cl,0
      mov dx,offset kb_buffer
      mov ah,10
      int 21h
lp:   mov si,dx
      mov al,[si]
      cmp al,23h
      je exit
      cmp al,'0'
      jb other
      cmp al,'9'
      ja other
      inc cl
other:inc,dx
      jmp lp
exit: mov nsum,cl
      mov ah,4ch
      int 21h
code ends
     end start