how to differentiate between when i press enter and write 0 in Assembly?

Question

Include Irvine32.inc

.data
prompt1 BYTE "Bye!", 0
prompt2 BYTE "Type an integer : ", 0

.code
MAIN PROC

    mov edx, OFFSET prompt2
    call WriteString

    call ReadInt

    exit
MAIN ENDP

end main

I would like to end the program when I just press enter key, And print value when I write integer value(-2^15 ~ 2^15-1).

I have a problem that I don't know how to let compiler differentiate when I write 0 value and press enter key. All of flags and registers value are same when I write 0 and press enter key. so I can't differentiate it on the code.

I could solve this problem when I call WriteChar and check whether first character is enter or not, but it was very complex code. When I wrote value in case calling WriteChar, I had to change value from string to integer.

Is there any easy way to solve this problem?

Answer 1

No way! You have to rewrite Irvine's ReadInt procedure.

The original function uses ReadString and stores the result in ECX. However, due to USES ecx edx the former value of ECX will be restored at the end of the procedure. Just to change it to USES edx solves the problem. ECX contains now the size of the inputted string.

Include Irvine32.inc

.data
prompt1 BYTE "Bye!", 0
prompt2 BYTE "Type an integer : ", 0
promptBad BYTE "Invalid input",0

.code
MAIN PROC

    mov edx, OFFSET prompt2
    call WriteString

    read:
    call myReadInt

    jo  error
    jecxz error

    call WriteInt
    exit

error:
    mov  edx,OFFSET promptBad
    call WriteString
    exit
MAIN ENDP

myReadInt PROC USES edx
LOCAL digitBuffer[50]:BYTE

    lea   edx, digitBuffer
    mov   ecx,50
    call  ReadString
    mov   ecx,eax   ; save length in ECX

    call    ParseInteger32  ; returns EAX, CF

    ret
myReadInt ENDP

end main