解答例

課題1

n = gets.to_i
for i in 0..n-1
  (n-i).times do
    print " "
  end
  (i*2+1).times do
    print "*"
  end
  puts
end

課題2

def myprime (n)
  i = 2
  until i*i > n
    return false if n%i == 0
    i += 1
  end
  return true
end

puts (if myprime gets.to_i then "yes" else "no" end)

課題3

def myprime (n)
  raise RuntimeError if n < 2
  i = 2
  until i*i > n
    return false if n%i == 0
    i += 1
  end
  return true
end

print "２以上の整数を入れてください:"
begin
  puts (if myprime gets.to_i then "yes" else "no" end)
rescue RuntimeError
  print "２以上の整数だと言ってるでしょうが！:"
  retry
end

課題4

x = []
loop do
  print '数値? '
  a = gets.to_i
  break if a == 0
  x.push(a)
end
while x.length > 0 do
  puts x.pop
end

課題5

dictionary = { 'dog' => '犬', 'cat' => '猫' }
loop do
  print '英語：'
  x = gets.chomp
  if dictionary[x]
    puts "日本語：#{dictionary[x]}"
  else
    print "#{x}の日本語訳を教えてください："
    y = gets.chomp
    dictionary[x] = y
  end
end

課題6

longest = ''
IO.foreach('words.txt') do |line|
  if longest.length < line.length
    longest = line
  end
end
puts longest

課題7

def arraycalc(x, y)
  result = []
  while x.length > 0
    result << (yield x.shift, y.shift)
  end
  result
end

課題8

class Account
  attr_reader :balance
  def initialize
    @balance = 0
  end
  def deposit(n)
    @balance += n
  end
  def withdraw(n)
    if @balance >= n
      @balance -= n
      true   # 引き出し成功
    else
      puts "残高不足です。"
      false  # 引き出し失敗
    end
  end
  def transfer(x, n)
    if withdraw(n)  # 自分の口座から引き出せれば
      x.deposit(n)  # 相手の口座に入金する
    end
  end
end

課題9

class Student  # 同じ名前のクラス宣言は、追加されていく
  def affiliation
    university + faculty
  end
end