[ASM] MASM compare uninitialized buffers

Question

Hello everybody, I'm stuck writing my program Here's what I wanted it to do:

1. display a welcome message inside a console
2. Wait for the user to imput a number from 0 to 9]
3. compare that number to 0
4. display a message if it is, else exit

Here is what I currently have:

.386
.model flat,stdcall
option casemap:none
include \masm32\include\windows.inc
include \masm32\include\kernel32.inc
includelib \masm32\lib\kernel32.lib
include \masm32\include\user32.inc
includelib \masm32\lib\user32.lib
include \masm32\include\masm32.inc
includelib \masm32\lib\masm32.lib

.data
capt db "SCHiM says: ",0
txt       db "Enter a number 0-9:",0

.data?

data db ?

.code

start:


call AllocConsole

push offset txt
call StdOut

push 1
push offset data
call StdIn

mov al, data

cmp al, 0h
jz eqzero

invoke ExitProcess, NULL

eqzero:

push offset capt
call StdOut
push offset data
call StdOut

endloop:
jmp endloop

invoke ExitProcess, NULL
end start 

The program assembles & links perfectly without any warnings or errors But cmp always returns 1, if I print the value in data (with StdOut) it shows me the exact value I've put in. So why isn't it working?

Thanks in advance

Answer 1

You are probably moving the address of data to al somehow. Try mov al, [data] to get the value stored at data.

Answer 2

Try this:

cmp al, '0'

-or-

cmp al, 48

Why? Because you are interested in character '0', not numeric 0. Character '0' is encoded as 48 in most encodings.