Learn to Program

Chapter 05.markdown

Chapter 2

Each one builds on the previous, ie. I re-use constants defined earlier.

Hours in a year

HOURS_IN_DAY = 24
DAYS_IN_YEAR = 365.242199
HOURS_IN_YEAR = HOURS_IN_DAY * DAYS_IN_YEAR
puts "Hours in an astronomical year: #{HOURS_IN_YEAR}"

Minutes in a decade

MINUTES_IN_HOUR = 60
MINUTES_IN_DECADE = 10 * MINUTES_IN_HOUR * HOURS_IN_YEAR
puts "Minutes in a decade: #{MINUTES_IN_DECADE}"

Your age in seconds

require 'date'
BIRTH_DATE = Date.new(1971,6,6)
SECONDS_IN_HOUR = 3600
SECONDS_IN_DAY = SECONDS_IN_HOUR * HOURS_IN_DAY
puts "My age in seconds: #{(Date.today - BIRTH_DATE).to_i * SECONDS_IN_DAY}"

Our dear author's age

AGE_IN_SECONDS = 1025 * 10**6
SECONDS_IN_YEAR = SECONDS_IN_DAY * DAYS_IN_YEAR
puts "Author's age: #{AGE_IN_SECONDS / SECONDS_IN_YEAR}"

Chapter 5

Full name greeting

names = []
%w/first second last/.each do |n|
  print "#{n.capitalize} name: "
  answer = gets.chomp
  names.push( answer ) if answer.length > 0
end

puts "Hello #{names.join(' ')}"

Bigger, better favorite number

print "What's your favorite number: "
answer = gets.chomp
puts "Don't you think #{ answer.to_i + 1 } is a bigger and better favorite number?"

Chapter 06.markdown

Chapter 6

Angry boss

print "Whaddya want? "
answer = gets.chomp
puts %/WHADDYA MEAN "#{answer.upcase}"?!? YOU'RE FIRED!!/

Table of contents

WIDTH = 80
CONTENTS = [
  { :title => "Getting Started", :page => 1 },
  { :title => "Numbers", :page => 9 },
  { :title => "Letters", :page => 13 }
]

puts "Table of Contents".center(WIDTH)

CONTENTS.each_with_index do |h,i|
  lhs = "Chapter #{i+1}:  #{h[:title]} "
  rhs = " page" + h[:page].to_s.rjust(3)
  puts lhs + rhs.rjust(WIDTH-lhs.length, '.')
end

Chapter 07.markdown

Chapter 7

99 Bottles of Beer on the Wall

i = START = 99
while i > 0
  b = i == 1 ? "" : "s"
  n = i-1
  c = "#{n} bottle#{n==1?'':'s'}"
  if i-1 == 0
    c = "no more bottles"
  end

  puts "#{i} bottle#{b} of beer on the wall, #{i} bottle#{b} of beer."
  puts "Take one down and pass it around, #{c} of beer on the wall."
  puts
  i -= 1
end

puts "No more bottles of beer on the wall, no more bottles of beer."
puts "Go to the store and buy some more, #{START} bottles of beer on the wall."

Deaf grandma

YEAR_B = 1930
YEAR_E = 1950

print "Hello dear.  "

answer = ''
while true
  print "What do you want? "
  answer = gets.chomp

  break if answer == 'BYE'

  if answer.match( /[a-z]/ )
    puts "HUH?!  SPEAK UP, SONNY!"
  else
    puts "NO, NOT SINCE #{YEAR_B + rand(YEAR_E-YEAR_B)}"
  end
  puts
end

puts "Bye dear."

Deaf grandma extended

YEAR_B = 1930
YEAR_E = 1950

print "Hello dear.  "

said_bye = 0

answer = ''
while said_bye < 3
  print "What do you want? "
  answer = gets.chomp

  if answer == 'BYE'
    said_bye += 1
  else
    said_bye = 0
  end
  if answer.match( /[a-z]/ )
    puts "HUH?!  SPEAK UP, SONNY!"
  else
    puts "NO, NOT SINCE #{YEAR_B + rand(1+YEAR_E-YEAR_B)}"
  end
  puts
end

puts "Oh, fine, bye dear."

Leap years

print "Start year: "
start_year = gets.chomp.to_i

print "End year: "
end_year = gets.chomp.to_i

start_year.upto(end_year) do |year|
  if year % 400 == 0 || ( year % 4 == 0 && year % 100 != 0 )
    puts year
  end
end

Chapter 08.markdown

Chapter 8

Building and sorting an array

puts "Enter as many words as you like, one per line.  Blank line to end."
arr = []

while(true) do
  input = gets.chomp
  break if input == ''
  if input.include? ' '
    puts "Just one word per line please."
    next
  end
  arr.push input
end

puts "Your words, sorted alphabetically."
puts arr.sort

Table of contents, revisited

Already how I did it :)

Chapter 09.markdown

Chapter 9

Improved ask method

def ask question
  while true
    puts question
    reply = gets.chomp.downcase
    if reply == 'yes' || reply == 'no'
      return reply == 'yes'
    else
      puts 'Please answer "yes" or "no".'
    end
  end
end

Old-school Roman numerals

@map = {
  1 => 'I',
  5 => 'V',
  10 => 'X',
  50 => 'L',
  100 => 'C',
  500 => 'D',
  1000 => 'M',
}

def roman_numeral num
  str = ''
  @map.sort.reverse.each do |decimal, roman|
    if( 0 < factor = num / decimal )
      str += roman * factor
      num %= decimal
    end
  end
  puts str
end

Modern Roman numerals

@map = {
  1 => 'I',
  4 => 'IV',
  5 => 'V',
  9 => 'IX',
  10 => 'X',
  40 => 'XL',
  50 => 'L',
  90 => 'XC',
  100 => 'C',
  400 => 'CD',
  500 => 'D',
  900 => 'CM',
  1000 => 'M',
}

def roman_numeral num
  str = ''
  @map.sort.reverse.each do |decimal, roman|
    if( 0 < factor = num / decimal )
      str += roman * factor
      num %= decimal
    end
  end
  puts str
end

Chapter 10.markdown

Chapter 10

Sorts

This was my first free-form sort.

def __sort arr
  i = 0
  while i < arr.length - 1
    if arr[i] > arr[i+1]
      arr[i], arr[i+1] = arr[i+1], arr[i]
      i -= 1 unless i == 0
    else
      i += 1
    end
  end
end

This is the recursive version, but it just recurses on the index, not really the spirit of recursion.

def __recursive_sort arr, i = 0
  return unless i < arr.length - 1

  if arr[i] > arr[i+1]
    arr[i], arr[i+1] = arr[i+1], arr[i]
    i -= 1 unless i == 0
  else
    i += 1
  end
  __rsort arr, i
end

Here's a different version, which is my implementation of the algorithm Chris outlines in Learn to Program using a holder array.

Notice that I have extracted the core processing out into pop_smallest that pops the smallest element off an array. I also simplify the processing in that method by swapping the suspect rather than having the third array to hold the "still unsorted" elements.

class Array
  def pop_smallest
    suspect = self.shift

    self.each_with_index do |elem,i|
      if elem < suspect
        suspect, self[i] = self[i], suspect
      end
    end
    suspect
  end
end

Notice how simple these methods become once the core pop_smallest is factored out.

def sort to_sort
  sorted = []

  until to_sort.length == 0
    sorted << to_sort.pop_smallest
  end

  sorted
end

The recursive version is even simpler.

def rsort to_sort
  return [] if to_sort.length == 0

  return [ to_sort.pop_smallest ] + rsort( to_sort )
end

Shuffle

def shuffle arr
  arr.each_index do |i|
    r = rand(arr.length)
    arr[r], arr[i] = arr[i], arr[r]
  end
end

Dictionary sort

def __dsort arr
  i = 0
  while i < arr.length - 1
    if arr[i].downcase > arr[i+1].downcase
      arr[i], arr[i+1] = arr[i+1], arr[i]
      i -= 1 unless i == 0
    else
      i += 1
    end
  end
end

Expanded english_number

Wedding number

Ninety-nine Bottles of Beer on the Wall

Chapter 11.markdown

Chapter 11

Safer picture downloading

Build your own playlist

Build a better playlist

Chapter 12.markdown

Chapter 12

One billion seconds!

Happy birthday!

Party like it's roman_to_integer 'mcmxcix'!

Birthday helper!

Chapter 13.markdown

Chapter 13

Extend the built-in classes

Orange tree

Interactive baby dragon

Chapter 14.markdown

Chapter 14

Even better profiling

Grandfather clock

Program logger

Better program logger