What is the error in this assembler sourse code?

It could be the that cx is changed in the int and calls.

changed code:

data segment
num1  Dw  ?
num2  Dw  ?

msg0  DB  'Enter positive decimal values or 999 to stop.$'
msg1  DB  'Value $'
msg2  DB  'Value 2:$'
msg3  DB  'Value 3:$'
msg4  DB  'Value 4:$'
msg5  DB  'Value 5:$'
msg6  DB  'Value 6:$'
msg7  DB  'Sorted values are:$'
msg8  DB  'End of program$'
data ends

working_storage  segment    stack
                 dw         100h    dup(?)
             working_storage  ends
             


code           segment
               assume cs:code,ds:data,ss:working_storage
               extrn putdec:proc,putcrlf:proc,getdec:proc,getchar:proc,putchar:proc


 
start: mov ax,data
       mov ds,ax
     
      mov si,0
      mov cx,6

            push cx                              ;save the cx value that could be destroyed by the(1)
                                                      ;int or call routines, In 16 bit dos only si,di,bx are
      mov bx,1                              ;"usually" preserved in calls and interrupt routines.
      mov Dx,offset msg0              
      mov ah,9h
      int 21h
      call putcrlf


repeat:mov Dx,offset msg1              
      mov ah,9h
      int 21h
      mov ax,bx
      call putdec
     
      call getdec  
      cmp  ax,999                    
      jae  finish                        ;watch out, cx is still on the stack
      add  nums[si],ax
      mov ax,nums[si]

            pop cx                              ;get the cx value back for the compare(2)

      inc si
      inc bx
      dec cx
      jnz repeat

      mov Dx,offset msg7              
      mov ah,9h
      int 21h
      call putcrlf
      mov cx,6

            push cx                              ;same as above(1)

check:mov bx,nums[si]
      mov dx,nums[si+1]
      cmp dx,bx
      ja next
      mov nums[si],dx
      mov nums[si+1],bx
      ;mov  num1,bx
      mov  ax,nums[si]
      call putdec
      call putcrlf
      mov  ax,nums[si+1]
      call putdec
      call putcrlf


next:
       mov ax,bx
       call putdec
       mov ax,dx
       call putdec

             pop cx                              ;see above(2)

       inc si
       dec cx
     jmp check

     
finish:mov Dx,offset msg8  

            pop cx                              ;to realign the stack. This is not really necessary
                                           ;because the ax,4c00h int 21h cleans up the stack

;            add sp,2                              ;this can also be used            

      mov ah,9h
      int 21h
      call putcrlf
       
      mov ax,4c00h
      int 21h      
code ends
end start