Validate and Normalize Text Inputs

Introduction

This is the second lesson of chapter 7 in the Strings section of PCAP-31-03 (18% of the score, 8 of the 40 items). It completes objective 3.3 with the family of isxxx() character tests, and it connects objectives 3.1 (Unicode) and 2.1 (exceptions) in the way real programs do: input arrives as text, must be checked, cleaned and converted, and may fail at any step.