Homework 4: Due  February  21, 2011

Ruby Programming, part 2

1. Ruby Hash

Write a Ruby script which creates a hash containing key-value pairs as shown in the following table:

After initializing the hash, the script should display all the known keys (use the keys method to return a list of the keys in a hash).

Then interactively display a prompt and read user input of a type of animal/object. In response, output the number of legs for that animal/object, or an appropriate message if the name is not found. If the name is not found, the user should be prompted to add the animal/object if desired, with an input number of legs and added to the hash. Any changes to the hash should be followed by a display of all keys as was done at the start of the program.

Input should not be case sensitive.

End of input is signaled by the user entering Ctrl-Z.

An example execution of the script could look similar to the following (user input in green):

Milking stool, Centipede, Millipede, Dog, Ant, Chicken

Choose an animal name  
dog
The Dog has 4 legs

Choose an animal name
slug
Couldn't find Slug, want to add it? y
How many legs? 0

Slug, Milking stool, Centipede, Millipede, Dog, Ant, Chicken

Choose an animal name
milking stool
The Milking stool has 3 legs

Choose an animal name
SLUG
The Slug has 0 legs

2. Ruby Regular Expressions

The file in words.zip contains more than 38,000 words, one per line. Write a Ruby script which prints the number of words in this file that:

a) contain the string 'sses'
b) begin with a 'b' and end with a 'k'
c) contain a 'b' interior to the word (not the first letter) and followed later in the word by a 'k' interior to the word (not the last letter)
d) contain a number (string of digits)
e) do not contain the any of the letters 'm' through 'z'

3. Parsing a Java Class

Write a Ruby script that processes a Java file as follows

a) Displays a list of all the identifiers in the file. Find the rules for properly formed Java identifiers and use this to define a regular expression. Exclude any reserved words (keywords) from the list since they are not allowed to be used as identifiers.
b) Display the contents of the file with all comments removed. Note that Java has three forms of comments.