Question

I need to increment a number so that the code will increment forever, but it stays zero.

Here is my code:

section .data
FORMAT: db '%c', 0
FORMATDBG: db '%d', 10, 0
EQUAL: db "is equal", 10, 0
repeat:
    push  ecx  ; just to print
    push  FORMATDBG ; just to print
    call  printf ; just to print
    add esp, 8 ; add the spaces
    inc ecx ; increment ecx
    cmp ecx, 0 ; compare ecx to zero
    ja repeat ; if not equal to zero loop again

Answer 1

repeat:
    xor ecx, ecx
    push  ecx  ; just to print
    push  FORMATDBG ; just to print
    call  printf ; just to print
    add esp, 8 ; add the spaces
    inc ecx ; increment ecx
    cmp ecx, 0 ; compare ecx to zero
    ja repeat ; if not equal to zero loop again

xor ecx, ecx sets ecx to zero. I’m not sure if you know this. You probably do not want it to happen on each iteration. Furthermore your loop condition ja repeat currently causes a loop only if ecx > 0 which is probably not what you wanted (or is it?).

One last thing, printf probably trashes ecx (I am assuming cdecl or stdcall). Read up on call conventions (not sure what compiler/OS you are on) and see which registers are guaranteed to be preserved in function calls.

In terms of your code, you probably wanted something closer to this:

    xor ebx, ebx

repeat:
    push  ebx  ; just to print
    push  FORMATDBG ; just to print
    call  printf ; just to print
    add esp, 8 ; add the spaces
    inc ebx ; increment ecx
    cmp ebx, 0 ; compare ecx to zero
    ja repeat ; if not equal to zero loop again

This will not cause an infinite loop though. When ebx reaches its maximum value, its value will wrap around back to 0 which will cause the loop condition (ebx>0) to evaluate to false and your loop to be exited.