FIRST.txt

A simple, test-driven, object-oriented approach to converting Celsius to
Fahrenheit and vice-versa, hopefully it's simple enough to be useful for a
newcomer to programming.

gistfile1.rb

# Converts temperatures
class Temperature
  class NoUnitError < StandardError; end
  class NoDegreesError < StandardError; end

  # Store the input in an instance variable and checks its validity
  def initialize(string)
    @string = string.downcase
    raise NoUnitError.new unless unit
    raise NoDegreesError.new unless degrees
  end

  # Parse the degrees using a regular expression and String#match:
  # http://ruby-doc.org/core/classes/String.html#M000793
  def degrees
    if match = @string.match(/\d+/)
      match[0].to_i
    else
      nil
    end
  end

  # Parse the unit from the string, or returns nil.
  def unit
    case
    when @string.include?('f') then 'Fahrenheit'
    when @string.include?('c') then 'Celsius'
    else nil # This line is redundant, but it's good to be explicit
    end
  end

  # Converts Celsius values to Fahrenheit, or returns the same value if
  # already Fahrenheit
  def to_fahrenheit
    if unit == 'Fahrenheit'
      degrees
    else
      (9.0 / 5.0) * degrees + 32
    end
  end

  # Converts Fahrenheit value to Celsius, or returns the same value if
  # already Celsius
  def to_celsius
    if unit == 'Celsius'
      degrees
    else
      (5.0 / 9.0 * (degrees - 32.0))
    end
  end
end

# Runs the program.
if __FILE__ == $0
  print "Enter a temperature. (example: 32C or 43F): "

  begin
    temperature = Temperature.new($stdin.gets.chomp)
  rescue Temperature::NoDegreesError
    puts "You didn't the degrees value."
    exit 1 # Exits with an error status code
  rescue Temperature::NoUnitError
    puts "You didn't enter a valid unit (F or C)"
    exit 1 # Exits with an error status code
  end

  puts "Celsius:    #{temperature.to_celsius}"
  puts "Fahrenheit: #{temperature.to_fahrenheit}"
end

test.rb

require 'gistfile1'
require 'test/unit'

# Create a class to hold our test methods
class TemperatureTest < Test::Unit::TestCase

  # This is sort of advanced, but I wanted a prettier way of defining tests.
  def self.test(name, &blk)
    define_method("test " + name, &blk)
  end

  test "parsing degrees" do
    temperature = Temperature.new('32f')
    assert_equal 32, temperature.degrees
  end

  test "parsing units" do
    assert_equal 'Celsius',     Temperature.new('32C').unit
    assert_equal 'Fahrenheit',  Temperature.new('32F').unit
  end

  test "raises NoDegreesError when no degrees specified" do
    assert_raise Temperature::NoDegreesError do
      Temperature.new('C')
    end
  end

  test "raises NoUnitError when no unit specified" do
    assert_raise Temperature::NoUnitError do
      Temperature.new('32')
    end
  end

  test "Fahrenheit to Fahrenheit is same" do
    assert_equal 32, Temperature.new('32F').to_fahrenheit
  end

  test "Celsius to Fahrenheit converts degrees" do
    temp = 100
    correct_result = (9.0 / 5.0) * temp + 32
    assert_equal correct_result, Temperature.new('100C').to_fahrenheit
  end

  test "Celsius to Celsius is same" do
    assert_equal 100, Temperature.new('100C').to_celsius
  end

  test "Fahrenheit to Celsius converts degrees" do
    temp = 100
    correct_result = (5.0 / 9.0 * (temp - 32.0))
    assert_equal correct_result, Temperature.new('100F').to_celsius
  end

end