ReadDec PROC

   Reads a 32-bit unsigned decimal integer from standard input, stopping when the Enter key is pressed.
   All valid digits occurring before a non-numeric character are converted to the integer value.
   Leading spaces are ignored.

Call args:   None

Return args: If CF=0, EAX = valid binary value, and SF=sign.
             If CF=1, EAX = 0 input is invalid (blank or larger than 2^32-1).

Example:

.data
decNum    DWORD ?
promptBad BYTE "Invalid input, please enter again",0

.code
read:  call ReadDec
       jnc  goodInput

       mov  edx,OFFSET promptBad
       call WriteString
       jmp  read        ;go input again

goodInput:
       mov  decNum,eax  ;store good value