Questions

1. Write a regular expression to match dates in dd/mm/yyyy format. Is it possible to write this regular expression so that it only allows legal dates?
2. Explain the difference between the return value that yylex() returns to the caller, the lexeme that yylex() leaves in yytext, and the token value that yylex() leaves in yylval.
3. Not all the yylex() regular expressions return an integer category after they match. When a regular expression does not return a value, what happens?
4. Lexical analysis has to deal with ambiguity and it is entirely possible to write several regular expressions that all can match at a given point in the input. Describe Flex's tie-breaking rules for when more than one regular expression can match at the same place.