Added a basic-user-interaction example using `printf`, `atoi` and `get_user_string`.

[vvhitespace] / examples / basic-user-interaction / hello.pvvs

@ This example uses printf to print a string containing two user inputs of type
@ string and integer, both supplied by the user at runtime.

A"Hello, %s! In a trusting world, %u is older than I am.\n"

A"What is your name?\n"
SSSSN               | PUSH 0
NSTTSSSN            | JSR > 1000 (printf)
SSSTSSSSSSSSSSSSN   | PUSH 0x1000 (buf_size)
SSSTSSSSSSSSSSSSN   | PUSH 0x1000 (buf_addr)
NSTTSSSTSN          | JSR > 100010 (get_user_string)

A"How old age you?\n"
SSSSN               | PUSH 0
NSTTSSSN            | JSR > 1000 (printf)
SSSTSSSSSSSSSSSSN   | PUSH 0x1000 (buf_size)
SSSTSSSSSSSSSSSSSN  | PUSH 0x2000 (buf_addr)
NSTTSSSTSN          | JSR > 100010 (get_user_string)
SSSTSSSSSSSSSSSSSN  | PUSH 0x2000 (buf_addr)
NSTTTSSSSN          | JSR > 110000 (atoi)
SNN                 | DROP

SSSTSSSSSSSSSSSSN   | PUSH 0x1000 (buf_addr)

SSSTSN              | PUSH 2

NSTTSSSN            | JSR > 1000 (printf)

NNN                 | Terminate program

#include <stdio.pvvs>
#include <string.pvvs>
#include <convert.pvvs>