Entering a non-integer into an unsigned integer using scanf in NASM causing problems in loops - nasm

Question

Whenever I try entering a letter or symbol into my scanf for unsigned integers after previously entering an accepted number previously in the loop, it continually enters the previous number, causing the program to run indefinitely. How do I fix this? Here's an example code I wrote:
[bits 32]
global _main
extern _scanf
extern _printf
section .data
prompt_number db "Please select a number. Enter 0 to escape. ", 0
display_number db "You entered %u. ", 0
number_fmt db "%u", 0
number_input dd 0
section .bss
section .text
_main:
push ebp
mov ebp, esp
and esp, 0xfffffff0
_Label:
sub esp, 16
mov dword[esp], prompt_number
call _printf
add esp, 16
sub esp, 16
mov dword[esp], number_fmt
mov dword[esp+4], number_input
call _scanf
add esp, 16
sub esp, 16
mov dword[esp], display_number
mov eax, [number_input]
mov dword[esp+4], eax
call _printf
add esp, 16
cmp dword[number_input], 0
jne _Label
mov esp, ebp
mov eax, 1
pop ebp
ret

Answer 1

This is to do with how scanf operates in these circumstances, and a solution is to port one of the suggested solutions for Good way to flush scanf buffer when invalid entry entered from C.
My understanding is that if scanf can't map the input into the format string (in this case trying to convert an arbitrary character into an unsigned integer), then it gives up but doesn't remove anything from the input buffer. Thus, in this case, subsequent calls to scanf just use what is currently in the buffer.
Below is a quick attempt at porting the first solution (using getchar to consume the buffer). I can't vouch for its quality; this is basically my first run through programming assembly:
[bits 32]
global _main
extern _getchar
extern _scanf
extern _printf
section .data
prompt_number db "Please select a number. Enter 0 to escape. ", 0
display_number db "You entered %u. ", 0
scan_error db "Error scanning input. ", 0
number_fmt db "%u", 0
number_input dd 0
section .bss
section .text
_main:
push ebp
mov ebp, esp
and esp, 0xfffffff0
_Label:
sub esp, 16
mov dword[esp], prompt_number
call _printf
add esp, 16
sub esp, 16
mov dword[esp], number_fmt
mov dword[esp+4], number_input
call _scanf
add esp, 16
cmp eax, 0
jne _ScanSuccess
_ScanError:
sub esp, 16
mov dword[esp], scan_error
call _printf
add esp, 16
_ScanErrorConsumeInput:
sub esp, 16
call _getchar
add esp, 16
cmp eax, -1 ; most common value indicating end-of-file
je _Label
cmp eax, 10 ; newline in ASCII
je _Label
jmp _ScanErrorConsumeInput
_ScanSuccess:
sub esp, 16
mov dword[esp], display_number
mov eax, [number_input]
mov dword[esp+4], eax
call _printf
add esp, 16
cmp dword[number_input], 0
jne _Label
_Return:
mov esp, ebp
mov eax, 1
pop ebp
ret