Assembly , moving through an array

Question

I have an array where I have to add all two digit numbers, the part with the 2 digit number sorting works , but I can't seem to take the next digit from my array it always takes the first one

.386
.model flat,stdcall
.stack 4096
ExitProcess proto,dwExitCode:dword


.data 

skaic DWORD 15,20,12,11,15151515
suma DWORD ?
.code

main proc
mov ecx, 0

l1:
    mov ebx,skaic
    add ebx,ecx

    cmp ebx,15151515
    je endl1

    add ecx, 4
    mov eax,ebx
    cmp eax,9
    jng l1

    add suma, eax
    mov eax, 0
    mov ebx, 0
    jmp l1

endl1:


    invoke ExitProcess,0
main endp
end main

enter image description here

You did not even load a single item from the array. You are missing mov ebx, [ebx]. Could of course be rewritten more efficiently. PS: this looks more like masm than nasm. — Jester
– Jester, Commented Oct 15, 2022 at 12:55
Have you looked at this in the debugger? What value are you seeing in ebx, say at the cmp .. 1515? — Erik Eidt
– Erik Eidt, Commented Oct 15, 2022 at 12:57
thank youuuuu it finally works now I'll try to do a few more to actually find out how everything works thoroughly — VIGEEDUN
– VIGEEDUN, Commented Oct 15, 2022 at 13:05
so offset is sending the address of the array, is it possible to somehow , take the last digit of array? because I want to compare the eax to last digit of array and je endloop1 — VIGEEDUN
– VIGEEDUN, Commented Oct 15, 2022 at 13:19

Sep Roland · Accepted Answer · 2022-10-16 00:47:49Z

Since this is MASM code, the mov ebx, skaic instruction is retrieving the first element of the array. However seeing the addition with the ECX register and how you raise ECX by 4 throughout the loop, clearly indicates that you expect EBX to contain an address at the same time. It can't be both at once!
The good solution is to maintain a simple pointer that starts by pointing at the first element of the array, and that is incremented by 4 on each iteration of the loop.

    mov  ebx, OFFSET skaic  ; Pointing at the first element
T1:
    mov  eax, [ebx]         ; Retrieving the current element
    add  ebx, 4             ; Preparing for the next element
    cmp  eax, 15151515      ; Is it the array terminator
    je   endT1              ; Yes
    cmp  eax, 10
    jb   T1                 ; Has fewer than 2 digits, so don't add
    add  suma, eax
    jmp  T1
endT1:

Tip1: Don't use label names like l1. These are hard to read! The mention T1 is already a better choice amongst the non-descriptive label names...
Tip2: It would be a good idea to also insert some array elements that have fewer than 2 digits. If all the array elements have 2 digits, how will you verify that the "number sorting works" ?

From a comment:

... is it possible to somehow , take the last digit of array? because I want to compare the eax to last digit of array and je endloop1

Because the skaic array holds 5 dwords, the last element (we don't talk about 'digit' in this respect), is located at skaic + 16. The offset is 16 because there are 4 elements of each 4 bytes that come before the last element.
In code: cmp eax, [skaic + 16] je endT1.

Alternatively, because the suma variable follows the skaic array directly in memory, the last element is also found at suma - 4.
In code: cmp eax, [suma - 4] je endT1.

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