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Assembly Discussion Thread
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Oct 1st, 2009

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printing a digit (as a character)

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Hello!
I'm kind of new in assembly programming and I've been struggling with the following problem today:
How to print an integer, using BIOS interrupt 10h, with its 0Eh in AH register, as its function to print a character to the screen...

For example, how to print the last digit of 2005.
here's what I've tried, using division by 10:

Assembly Syntax (Toggle Plain Text)
mov ax, 2005
mov cx, 10
div cx     ; now, AH should contain the remainder (5) and AL = 200
mov al, ah ; because AL should contain the character to print
add al, 48 ; because ASCII code for 5 is 53 (decimal).
mov ah, 0Eh; the function for the 10h interrupt
int 10h
mov ax, 2005
mov cx, 10
div cx     ; now, AH should contain the remainder (5) and AL = 200
mov al, ah ; because AL should contain the character to print
add al, 48 ; because ASCII code for 5 is 53 (decimal).
mov ah, 0Eh; the function for the 10h interrupt
int 10h

I can't understand why 0 is printed to the screen instead of 5. If i change the line

Assembly Syntax (Toggle Plain Text)
add al, 48
to
add al, 49
add al, 48
to
add al, 49

it prints out 1.
... am I missing something? is it because I use decimal format for integers instead of the hexadecimal one?

Thank you in advance!

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andreib

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Oct 1st, 2009

Re: printing a digit (as a character)

I'm replaying to my post...

I've found the answer to the problem while posting the question and running the code on my computer... I hope I did well by posting it, maybe someone is having the same integer printing related issue.

The thing is I had to write

Assembly Syntax (Toggle Plain Text)
mov cl, 10
div cl
mov cl, 10
div cl

because with whole CX instead of its low part (CL), after division the remainder is stored somewhere else (I think in DX, and it's not the right one anyway...) so, in the instruction below

(Toggle Plain Text)

DIV source

I should have a 8-bit source.

sorry for bothering

andreib

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Oct 1st, 2009

Re: printing a digit (as a character)

2005 - 2000 = 5 / 1 = 5 got it???
The actual value of the asci characte '5' is 0x35,
well there you go!

Understanding the DIV instruction:
DIV reg16 = DX:AX / reg16 = quotient AX remainder DX
DIV reg8 = AX / reg8 = quotient AL remainder AH

NotNull

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