Chapter 3

1. A first approximation of the regular expression is [0-3][0-9]"/"[01][0-9]"/"[0-9]{4}. While it is possible to write a regular expression that matches only legal dates, such an expression is impractically long, especially considering leap years. In such cases, it makes sense to use the regular expression that provides the simplest close approximation of correctness, and then check correctness in the semantic action or a subsequent semantic analysis phase.
2. yylex() returns an integer category for use in syntax analysis, while yytext is a string that contains the symbols matched and yylval holds an object called a token that contains all the lexical attributes of that lexeme.
3. When a regular expression does not return a value, the characters that it matched are discarded and the yylex() function continues with a new match, starting with the next character in the input.
4. Flex matches the longest string that it can; it breaks ties among multiple...