Addition of two numbers from user input using FASM

Question

I have successfully got the user's input and placed into bl and bh, but when i attempt to add them together, the result is not in decimal form even if I already added '0' to the result. Any ideas on how to solve this problem? Thanks

org 100h

mov ah, 9
mov dx, msg
int 21h

mov ah, 1
int 21h

mov [number], al
mov bl, [number]

mov ah, 2
mov dl, 0ah
int 21h

mov ah, 9
mov dx, msg2
int 21h

mov ah, 1
int 21h

mov [number], al
mov bh, [number]

add bh, bl
add bh, 30h

mov ah, 2
mov dl, 0ah
int 21h

mov ah, 9
mov dx, sum
int 21h

mov ah, 2
mov dl,bh
int 21h

mov ax, 4C00h
int 21h

msg db 'Enter first number: ', 24h
msg2 db 'Enter second number: ',24h
sum db 'The sum is: ',24h
number db 0

If you're not very good at programming I suggest not using assembly. You don't seem to understand well the relation between number (digit) and its ASCII representation. — user202729, Feb 04 '18 at 07:09
@user202729 : comments like your are what make Stackoverflow a poor place to get help. Did you consider he might be a student given an assignment? Learning assembly in one form or another, even for older processors is very common in academia in certain parts of the world. — Michael Petch, Feb 04 '18 at 07:12
@MichaelPetch ... then the OP's teacher must have taught carefully about that before giving the assignment. — user202729, Feb 04 '18 at 07:13
@user202729 : I suggest you find another site where you can troll the users. — Michael Petch, Feb 04 '18 at 07:14
you're right michael. I am a student given an assignment. And as of now, I am not that good in assembly. Do you have any ideas on how to solve this one ? — Karl Philipp Sy Fabre, Feb 04 '18 at 07:15
Consider the issue. What happens if you add 9 and 9 together. The result is higher than 10. It is 18. You have to write code that converts a multidigit value to a string. I suspect that is what is causing your issue. If that is the issue, there are other answers on SO related to this. — Michael Petch, Feb 04 '18 at 07:16
@user202729: If you cannot help then stop commenting here, hope you understand. — Karl Philipp Sy Fabre, Feb 04 '18 at 07:16
@MichaelPetch: my assignment is to add single digits resulting to single digit answer only :) sorry i forgot to put that info — Karl Philipp Sy Fabre, Feb 04 '18 at 07:17
@MichaelPetch: yes mike, because later we are going to deal with that — Karl Philipp Sy Fabre, Feb 04 '18 at 07:19

user202729 · Accepted Answer · 2018-02-04T07:26:41.293

3

You seems to misunderstood the relation between ASCII codes and values.

Assume the user input 34. With your code, you set bl to the ASCII value of the character 3 (which is 0x33) and bh to the ASCII value of the character 4 (0x34).

Now, to add them together, you need to convert them into values. By subtracting 0x30.

sub bl, 30h
sub bh, 30h

Now bl = 3, bh = 4. just add them together.

add bh, bl

Now bh = 7. Convert it to ASCII value of the digit and display it to the user. That part you already did it correctly.

add bh, 30h
...

In summary:

After read a digit, subtract it by 30h.
Before printing a digit, add 30h to it.

edited Feb 04 '18 at 07:26

answered Feb 04 '18 at 07:20

user202729

3,358
3
25
36

Thank you! now its working. I'm sorry to disturb you – Karl Philipp Sy Fabre Feb 04 '18 at 07:28
1

Because you subtract 2·0x30 and then add 0x30, you just could subtract 0x30 for some little optimisation. :) – sivizius Feb 04 '18 at 10:50

Addition of two numbers from user input using FASM

1 Answers1