audio_form, or input_box?
If I need to avoid using input_box (say, because it would break a network connection), I'd probably write my own text edit function out of shere not-feeling-like-it with those that already exist.
But there are plenty out there.

Just use string_to_number on the result.

The main problem is: you can't block your entire game waiting for a player input, or the network connection will fail. The audio form is a non-blocking system with a unique audio_form class, which simulates real forms

This class only handle the "form part" : you have to set the default values of fields, etc.
The simple BGT example of the BGT help for input_box is:

#include "form.bgt"

audio_form form;

void main()
{
form.create_window("Example Form", true);
int name=form.create_input_box("&Name");
int password=form.create_input_box("&Password", "", "*");
int message=form.create_input_box("&Message", "This is a read only input box.", "", 0, true);
int ok=form.create_button("OK");
int cancel=form.create_button("E&xit");
while(true)
{
form.monitor();
wait(5);
if(form.is_pressed(ok))
{
exit();
}
if(form.is_pressed(cancel))
{
exit();
}
if((key_down(KEY_LMENU))&&(key_pressed(KEY_F4)))
{
exit();
}
}
}

This is a useless code but you can look at it to understand how it works. The BGT help explains almost everything about the audio form class. The main problem is : how to focus all player controls on this form, without blocking the program in something like a loop, which would break the network connection? That's what you really have to think about I think