 # paulfioravanti's solution

## to Hexadecimal in the Ruby Track

Published at Jul 13 2018 · 0 comments
Instructions
Test suite
Solution

Convert a hexadecimal number, represented as a string (e.g. "10af8c"), to its decimal equivalent using first principles (i.e. no, you may not use built-in or external libraries to accomplish the conversion).

On the web we use hexadecimal to represent colors, e.g. green: 008000, teal: 008080, navy: 000080).

The program should handle invalid hexadecimal strings.

For installation and learning resources, refer to the exercism help page.

For running the tests provided, you will need the Minitest gem. Open a terminal window and run the following command to install minitest:

``````gem install minitest
``````

If you would like color output, you can `require 'minitest/pride'` in the test file, or note the alternative instruction, below, for running the test file.

Run the tests from the exercise directory using the following command:

``````ruby hexadecimal_test.rb
``````

To include color from the command line:

``````ruby -r minitest/pride hexadecimal_test.rb
``````

## Source

All of Computer Science http://www.wolframalpha.com/examples/NumberBases.html

## Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

### hexadecimal_test.rb

``````require 'minitest/autorun'
require_relative 'hexadecimal'

class HexadecimalTest < Minitest::Test
def test_hex_1_is_decimal_1
assert_equal 1, Hexadecimal.new('1').to_decimal
end

def test_hex_c_is_decimal_12
skip
assert_equal 12, Hexadecimal.new('c').to_decimal
end

def test_hex_10_is_decimal_16
skip
assert_equal 16, Hexadecimal.new('10').to_decimal
end

def test_hex_af_is_decimal_175
skip
assert_equal 175, Hexadecimal.new('af').to_decimal
end

def test_hex_100_is_decimal_256
skip
assert_equal 256, Hexadecimal.new('100').to_decimal
end

def test_hex_19ace_is_decimal_105166
skip
assert_equal 105_166, Hexadecimal.new('19ace').to_decimal
end

def test_invalid_hex_is_decimal_0
skip
assert_equal 0, Hexadecimal.new('carrot').to_decimal
end

def test_black
skip
assert_equal 0, Hexadecimal.new('000000').to_decimal
end

def test_white
skip
assert_equal 16_777_215, Hexadecimal.new('ffffff').to_decimal
end

def test_yellow
skip
assert_equal 16_776_960, Hexadecimal.new('ffff00').to_decimal
end
end``````
``````# frozen_string_literal: true

class Hexadecimal
HEX_DIGITS = "0123456789ABCDEF"
private_constant :HEX_DIGITS
HEX_STRING = /\A[#{HEX_DIGITS}]+\z/
private_constant :HEX_STRING
BASE = 16
private_constant :BASE

def initialize(string)
@string = string.upcase
end

def to_decimal
return 0 unless string.match?(HEX_STRING)
string.chars.reverse.each.with_index.sum(&method(:hex_to_dec))
end

private

attr_reader :string

def hex_to_dec((hex_character, exponent))
HEX_DIGITS.index(hex_character) * BASE**exponent
end
end``````

## Community comments

Find this solution interesting? Ask the author a question to learn more.

### What can you learn from this solution?

A huge amount can be learned from reading other people’s code. This is why we wanted to give exercism users the option of making their solutions public.

Here are some questions to help you reflect on this solution and learn the most from it.

• What compromises have been made?
• Are there new concepts here that you could read more about to improve your understanding?