4 - String: Boundary checking on index and subtring operators
5 - String: test cases for numerical conversion
6 - String: Implement String != regex operator
7 - String: index and rindex methods with String argument
9 - date: test parser for invalid dates and syntax errors
10 - date: Parser for stream input
11 - date: Weekday and week number
13 - Include classes: UTC, complex, integer
14 - UTC: Convert to and from time_t, struct tm