Arithmetic operations in ASM Language

Question

I just need some help. I don't fully understand and I am fairly new to masm32 so if you could explain, that would be great!

MOV AX, 200
ADD AX, 300
MOV RESULT, AX

Will result be equal to 500? I tried adding 3 and 2 and using this to show output:

MOV DX, RESULT
ADD RESULT, '0'
MOV AH, 02H
INT 21H

But the output is a candy cane character! Where is it wrong?

Now I assume subtraction will work the same as addition, so on to Multiplication we go. This is what I did for multiplication

MOV AX, 30
MOV BX, 8
MUL BX
MOV RESULT, AX

Is RESULT's value equal to 240?.... I tried AX as 3 and BX as 2. The output is a spade. Can you point me to the right direction?

Now division.

MOV AX, 30
MOV BX, 12
DIV BX
MOV RESULT, AX

What holds the quotient? If what I read was correct, that would be AX, and DX holds the remainder...?

I have already done 8 bit arithmetic (using AL, BL, DL...) and I tried to apply it here, sadly, when the RESULT becomes greater than 128, it just outputs garbage. Someone suggested that I should declare my variables as 'RESULT dw ?' instead of 'RESULT db ?' and instead of AL BL registers I should use AX BX.... Now I'm stuck.

Any help would be appreciated! Sorry if these questions seem too trivial. Anyway, thanks in advance! :DD

Answer 1

MOV AX, 200
ADD AX, 300
MOV RESULT, AX
Will result be equal to 500?

Yes.

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I tried adding 3 and 2 and using this to show output:
MOV DX, RESULT
ADD RESULT, '0'
MOV AH, 02H
INT 21H
But the output is a candy cane character! Where is it wrong?

You're adding '0' to RESULT after moving RESULT to DX. You should probably add '0' to DL instead of to RESULT.

---

Now division.
MOV AX, 30
MOV BX, 12
DIV BX
MOV RESULT, AX
What holds the quotient? If what I read was correct, that would be AX, and DX holds the remainder...?

DIV BX divides the 32-bit value DX:AX by BX, so you should clear DX before the division. The quotient will end up in AX and the remainder in DX.

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Someone suggested that I should declare my variables as RESULT dw ?

If you're going to move 16-bit values to/from the variable (e.g. MOV RESULT,AX) then you should make the variable (at least) 16 bits.