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-   -   I need help !!!!!!!!!!!!!!!!!!!!!!!!!! (http://www.go4expert.com/forums/i-need-help-t6074/)

duynguyenvan 28Aug2007 14:08

I need help !!!!!!!!!!!!!!!!!!!!!!!!!!
 
Hello,
Could you pls help me answer this question:
- Please take a look at my small Assembly program that reads a tring from keyboard, then displays all the characters that are not uper-case letters in reverse order:
Code:

.model small
.stack 100
.data
        tb1 db 'Pls enter a string, enter to finish $'
        tb2 db 10,13,'The characters that are not uper-case : $'
        xau db 80 dup(?)
.code
Main proc
        mov ax,@data
        mov ds, ax
        mov es, ax
        mov ah,9
        lea dx,tb1
        int 21h
        xor cx,cx
        lea di,xau
nhap:        mov ah,1
        int 21h
        cmp al,13
        je thoi
        cmp al,'A'
        jb dung
        cmp al,'Z'
        ja dung
        jmp nhap
dung:        stosb
        inc cx
        jmp nhap
thoi:        mov ah,9
        lea dx,tb2
        int 21h
        dec di
        mov si,di
        std
        mov ah,2
quay:        lodsb       
        mov dl,al
        int 21h
        loop quay
        mov ah,4ch
        int 21h
Main endp
        End main

The code above runs very well, even though i did not use the Clear Direction Flag (cld) instruction after the instruction in red (lea di,xau)
The string processing is still in forward direction.
The question is that: Why?

I appreciate your help. my email: duyngv@us.ibm.com

Regards,
Duy.

duynguyenvan 28Aug2007 14:34

Re: I need help !!!!!!!!!!!!!!!!!!!!!!!!!!
 
Is there any instructions in the ones below that impact on the Direction Flag so that the DF always set to 0 :
Code:

ea dx,tb1
int 21h
xor cx,cx
lea di,xau
nhap: mov ah,1
int 21h
cmp al,13
je thoi
cmp al,'A'
jb dung
cmp al,'Z'
ja dung
jmp nhap
dung: stosb
inc cx
jmp nhap


jwshepherd 28Aug2007 15:11

Re: I need help !!!!!!!!!!!!!!!!!!!!!!!!!!
 
nhap: mov ah,-1

shabbir 28Aug2007 15:26

Re: I need help !!!!!!!!!!!!!!!!!!!!!!!!!!
 
duynguyenvan, there are lots of things I would like to tell you.

1. have code blocks when you have code snippets in the posts.
2. Have a title that describes your content.
3. Don't just jump into every thread and have the same post.
4. Be patient for a reply.

I would suggest you read Hints before you make a query.

duynguyenvan 28Aug2007 15:43

Re: I need help !!!!!!!!!!!!!!!!!!!!!!!!!!
 
Hi jwshepherd,
what do you mean?
do you mean the line:
nhap: mov ah,1
in my code set the DF to 0 so that the di will always point to a continuous character? like we use the cld instruction?

duynguyenvan 28Aug2007 15:44

Re: I need help !!!!!!!!!!!!!!!!!!!!!!!!!!
 
Dear Shabbir, i'm so sorry for that !

duynguyenvan 5Sep2007 17:34

Re: I need help !!!!!!!!!!!!!!!!!!!!!!!!!!
 
seems there is no one knows about this stuff ... :(


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