菜鸟提问：这个程序无法循环是为什么啊？

DATA SEGMENT
INPUT DB 0AH,0AH,'PLEASE INPUT A NUMBER:'
ERROR  db  0ah,0dh,'INPUT ERROR!';0ah,0dh是字符型2个字符，是回车换行符
BUF  DB 10
      DB ?
      DB 10 DUP(0)
ARR    DD 2 DUP(0)
DATA ENDS
CODE SEGMENT
         ASSUME CS:CODE,DS:DATA
START:MOV AX,DATA
       MOV DS,AX

                                       
       mov ah,08H                                            ;dos调用的8号功能:不需要提供入口参数，等待键盘输入一个字符。自动将ASCII码存入AL中
          int 21h
        
    CMP AL,30
    JB A1
    CMP AL,39
    JA A1

        mov BL,AL
        MUL BL
        XOR BH,BH
        MUL BL
      
        CMP AX,0FFH
        JA     A
B1:        DIV 10
            MOV BL,AL
            PUSH AH
            CMP BL,0
            INC CX
            JNE B1   
            JMP  A2
A:            DIV 10
            PUSH DX
B2:        DIV 10
            MOV BL,AL
            PUSH AH
            CMP BL,0
            INC CX
            JNE B2   

A1:  LEA  dx,error                      ;出错提示
      mov ah,9
      int 21h

    A2:POP AH
        LOOP A2
         MOV AH,4CH
        INT  21H
    CODE ENDS
              END START
 
 
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