x86 assembly (masm32) output multiplied number produces junk characters

Question

I'm coming back to assembly for the sake of it after a few months and I'm having trouble getting two numbers to multiply and output the result. Here's my code:

.386
.model flat, stdcall 
option casemap :none 

include \masm32\include\windows.inc 
include \masm32\include\kernel32.inc 
include \masm32\include\masm32.inc 
includelib \masm32\lib\kernel32.lib 
includelib \masm32\lib\masm32.lib

.data 
     sum sdword 0
.code 
start:
mov ecx, 6        
xor eax, eax                  
mov edx, 7               
mul edx                  
push eax
pop sum
lea eax, sum
call StdOut
push 0 
call ExitProcess
end start 

It outputs something like P &aeffiini,.

QUESTION: Why does it output that random character string, and how can I fix it?

Thanks in advance.

Answer 1

Because StdOut prints NULL terminated strings NOT numbers. You need to convert the number to a string first. MASM32 has dwtoa. Also, your multiplying wrong. you multiply with eax

include masm32rt.inc

.data?
lpBuffer    db 12 dup (?)

.code 
start:
    mov     ecx, 6        
    mov     eax, 7               
    mul     eax    

    push    offset lpBuffer
    push    eax
    call    dwtoa 

    push    offset lpBuffer             
    call    StdOut

    inkey
    push    0 
    call    ExitProcess
end start