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CSCI 305 Programming Languages

Ruby Part 1

Reading: Ruby Tutorial Sections 3, 5, 6, 7, 13, 14, and 15

Installing Ruby: You can install ruby using instructions found at the following sites:

• Windows
• Mac
• Linux

Outside of Class

Watch this Video - (1:35:29)

OR

Watch these videos (the above video broken into 6 parts for easier consumption):

• Part 1 (15:46)
• Part 2 (15:18)
• Part 3 (15:46)
• Part 4 (16:56)
• Part 5 (13:26)
• Part 6 (18:23)

Explore Ruby:

• Find the following things:
  • The Ruby API
  • The free online version of “Programming Ruby: The Pragmatic Programmer’s Guide”
  • A method that substitutes part of a string
  • Information about Ruby’s regular expressions
  • Information about Ruby’s ranges
• Do the following things:
  • Print the string “Hello, World”
  • For the string “Hello, Ruby”, find the index of the word “Ruby”
  • Print your name 10 times
  • Print the string “This is sentence number 1” where the number 1 changes from 1 to 10.
  • Run a Ruby program from a file

Outline:

• Interactive ruby
  • Hello World!
  • Basic Expressions
  • Decisions
  • Global Variables
  • What is Truth?
• Ruby Scripts
  • Multiline Strings
  • Basic String Ops
  • Chomping Strings
  • Working with Strings
  • Numbers and Iteration
  • Arrays
  • Hashes
  • Control Structures
  • Methods
  • Methods
  • Methods
  • Blocks
  • Gets
  • Gets
  • Ranges
  • Illusions of Regex
  • songdata.txt

In class exercises Solutions Video (10:24):

Excercise 1:

Write a ruby program which prompts for and reads one line of input. It then echos the line, then prints it repeatedly, each time removing every second character. It continues until no more characters can be removed. Treat all characters alike; no special treatment for spaces or punctuation

isaac@sparqline001 $ ruby reduce.rb
Please enter a line> Sandy.
Sandy.
Sny
Sy
S
isaac@sparqline001 $ ruby reduce.rb
Please enter a line> On Tuesday, Frank in the motor pool buys lunch.
On Tuesday, Frank in the motor pool buys lunch.
O usa,Faki h oo olby uc.
OuaFk  oob c
Oak o
Oko
Oo
O
isaac@sparqline001 $ ruby reduce.rb
Please enter a line> Those so aglow point at hues afferent
Those so aglow point at hues afferent
Toes go on the feet
Te oo h et
T ohe
Toe
Te
T

Solution:

print "Please enter a line> "
line = gets.chomp

puts line

until line.length < 2
  new_line = ""
  (0..(line.length - 1)).step(2) do |i|
    new_line += line[i]
  end

  puts new_line
  line = new_line
end

Exercise 2 (A Solution):

Write a quick ruby script to determine if a word is a palindrome. This script should prompt the user for a single line of input and then echo the input, its reverse, and then whether or not it is a palindrome (regardless of case).

isaac@sparqline001 $ ruby palindrome.rb
Please enter a word> Bob
Bob
boB
Bob is a palindrome

Modification (A Solution)

Modify Exercise 2 such that if given a string with multiple words that forms a single palindrome when spaces are removed, you can detect that as well. Echo out the space reduced form of the line, its reverse, and whether or not it is a palindrome.

isaac@sparqline001 $ ruby palindrome2.rb
Please enter a line> Was it a car or a cat i saw
Was it a car or a cat i saw
was i tac a ro rac a ti saW
Wasitacaroracatisaw
wasitacaroracatisaW
The line is a palindrome

Solution:

def palindrome? str
  str == str.reverse
end

print "Enter a line> "
line = gets.chomp

puts line
puts line.reverse

line.gsub!(/\s/, '')
puts line
puts line.reverse

puts "#{line} is a palindrome" if palindrome? line.downcase