HW – Regular Expressions
CMSC 208
Spring 2015
1) Problem 5 on page 75 of the book.
2) Problems 13 and 14 on page 76 of the book.
3) Problem 16 parts a, b, and c on page 76 of the book.
4) Problem 17 parts a-e on page 76 of the book.
5) Alphabet = {A .. Z}
a. Give a regular expression for all words that have two vowels in them.
b. Give an automaton picture for the same language.
6) Consider the rules for valid identifiers in the C++ language.
remember.) Give a regular expression for identifiers in C++.
(Look them up if you do not
7) Define a “simple HW inequality” to be an expression that compares two integers, with either
side of the operator being an integer. Assume all identifiers are integers For example:
VALID:
varname < 15
15 >= varname
17 < 19
x2 < y3
INVALID
var < 15.0 --- not an integer
var >> 19 --- not a valid operator
x == 4 + 5 --- the arithmetic expression considered not
valid for this exercise.
a. What is the alphabet?
b. Give a regular expression to describe the language of “simple HW inequalities”.
c. Give an automaton picture for “simple HW inequalities”.
CMSC 208
HW – Regular Expressions
Spring 2015
EXTRA CREDIT) Consider “compound HW inequalities” that allow for the Boolean
connectors (and, or, not) as well as parentheses involving “simple HW inequalities”. EG:
VALID:
varname < 15
(varname < 15)
(15 < varname) and (varname <= 20)
not (x < y) or (z == w)
not ((x < y) or (z == w))
INVALID:
(varname < 15
--- mismatched parentheses
(varname << 15)
--- not a valid operator
not and (x < y) or (z == w)
--- invalid combination
a. Give a regular expression for “compound HW inequalities”. Use [ ] rather than parentheses in
the expression so that the () can be part of the alphabet.
b. Give an automaton picture for “compound HW inequalities”.
HINT:
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Try adding the parens first.
Then try adding the binary operators (and, or).
Then try adding the unary operator (not).
Partial credit available for each stage.