reading a BYTE as a DWORD in Masm

once again I'm doing MASM programming. I'm trying to write a procedure using the Irvine32 library where the user enters a string which is put into an array of BYTEs with ReadString. Then it loops over that arrray and determines if each character is a number. H开发者_开发问答owever, when I try

cmp [buffer + ecx], 30h

MASM complains about comparing two things that are not the same size. Is there anyway I could read the ASCII code in each BYTE in the array as a DWORD (or otherwise extract the ASCII value in each BYTE)?

Does this work?

cmp BYTE PTR [buffer + ecx], 30h

To extract a BYTE as a DWORD you can do something like this:

mov EAX, 0
mov AL, [pointer]

or even better (thanks Martin):

movzx EAX, [pointer]

getData PROC
    push ebp
    mov ebp, esp
    mov esi, [ebp + 12] ; offset of buffer
    mov ebx, [ebp + 8] ; where to write answer

    GETNUMBERSTRING:
    mov edx, esi
    mov ecx, BufferSize
    mov eax, 0
    call ReadString

    mov ecx, eax ; set size to loop counter
    cld

    mov edx, 0
    PROCESSSTRING:
    lodsb

    cmp al, 30h
    jl WRONG
    cmp al, 39h
    jg WRONG

    ; add digit into total edx
    sub al, 30h
    push eax ; multiply edx by 10
    push ecx
    mov eax, edx
    mov ecx, 10
    mul ecx
    mov edx, eax
    pop ecx
    pop eax

    push ebx ; add to the total
    movsx ebx, al
    add edx, ebx
    pop ebx

    loop PROCESSSTRING
    jmp DONE

    WRONG:
    call Crlf
    stringWriterEndl invalid
    jmp GETNUMBERSTRING

    DONE:
    mov [ebx], edx
    pop ebp
    ret 8
getData ENDP

That's what I needed to do.