Can't figure out how to print a number in MASM32

I hate asking such basic questions. It makes it look like I am being lazy! But I have spent hours looking over documentation, and for whatever reason, I can't get my head spun around straight on this small point.

I want to print the character "4" to the screen. I can do it as a string, but not from an ascii value.

Here is the working code:

include c:\masm32\include\masm32rt.inc
.data
    num4 db "4", 10,0
.code
start:
    invoke StdOut, addr num4
    inkey
    invoke ExitProcess, 0
end start

I just wanted to take a baby step from there and print ascii character 52 (which is "4"). Here's my best attempt so far:

include c:\masm32\include\masm32rt.inc
.data
.code
start:
    myvar db 52
    invoke StdOut, myvar
    inkey
    invoke ExitProcess, 0
end start

It assembles and links without trouble, but then crashes when I run it. I know that it doesn't have the 0 character at the end, but invoke StdOut, myvar,0 has too many arguments for StdOut.

My eventual goal is to be able to print a multiple digit number, as described by Alexey Frunze here:

x86 assembly (masm32) - how to split multi-digit data into individual characters

But since I am having so much trouble with syntax, I am taking baby steps. I found this, but it doesn't explain how to do the add 48 part syntactically:

x86 assembly - how to show the integer 2, not the second ASCII character

Please help me get past these opening hurdles, and thank you!

Solution

First, myvar db 52 is on the wrong place. When the program starts, the computer comes to db 52 and treats that as an instruction. Second, the 0 value (don't say character) is not an argument for StdOut and has to be at the end of the data. StdOut needs as argument a pointer to a zero-terminated string. You cannot give it a direct value, the function would take that as pointer nevertheless. BTW: Consider that StdOut is a function of MASM32 and not a function of the Windows kernel. Your program should look like:

include c:\masm32\include\masm32rt.inc
.data
    myvar db 52, 0
.code
start:
    invoke StdOut, ADDR myvar
    inkey
    invoke ExitProcess, 0
end start

You have first to build a string before outputting it with 'StdOut'. If you don't have a string but a number, you have to convert it to a string (keywords for Google: "assembly convert integer to ascii"). The trick is to repeatedly divide the number by 10 and store the remainder. Another trick is to use a MASM32-macro.

INCLUDELIB C:\masm32\lib\masm32.lib
INCLUDE C:\masm32\include\masm32rt.inc

.DATA
    decimalstr db 16 DUP (0)
    myvar db 52

.CODE

start PROC

    movzx eax, myvar         ; Load an 8-bit-byte into a 32-bit-register
    lea edi, decimalstr      ; Load the address of decimalstr
    call EAX_to_DEC
    invoke StdOut, addr decimalstr

    movzx eax, myvar
    printf ("\nAnd the lazy MASM32 way: %u\n",eax)

    invoke ExitProcess, 0
start ENDP

EAX_to_DEC PROC             ; ARG: EDI pointer to string buffer
    mov ebx, 10             ; Divisor = 10
    xor ecx, ecx            ; ECX=0 (digit counter)
  @@:                       ; First Loop: store the remainders
    xor edx, edx
    div ebx                 ; EDX:EAX / EBX = EAX remainder EDX
    push dx                 ; push the digit in DL (LIFO)
    add cl,1                ; = inc cl (digit counter)
    or  eax, eax            ; AX == 0?
    jnz @B                  ; no: once more (jump to the first @@ above)
  @@:                       ; Second loop: load the remainders in reversed order
    pop ax                  ; get back pushed digits
    or al, 00110000b        ; to ASCII
    stosb                   ; Store AL to [EDI] (EDI is a pointer to a buffer)
    loop @B                 ; until there are no digits left
    mov byte ptr [edi], 0   ; ASCIIZ terminator (0)
    ret                     ; RET: EDI pointer to ASCIIZ-string
EAX_to_DEC ENDP

END start

Also take a look here.