 # rootulp's solution

## to Binary in the CoffeeScript Track

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

#### Note:

This solution was written on an old version of Exercism. The tests below might not correspond to the solution code, and the exercise may have changed since this code was written.

Convert a binary number, represented as a string (e.g. '101010'), to its decimal equivalent using first principles.

Implement binary to decimal conversion. Given a binary input string, your program should produce a decimal output. The program should handle invalid inputs.

## Note

• Implement the conversion yourself. Do not use something else to perform the conversion for you.

Decimal is a base-10 system.

A number 23 in base 10 notation can be understood as a linear combination of powers of 10:

• The rightmost digit gets multiplied by 10^0 = 1
• The next number gets multiplied by 10^1 = 10
• ...
• The nth number gets multiplied by 10^(n-1).
• All these values are summed.

So: `23 => 2*10^1 + 3*10^0 => 2*10 + 3*1 = 23 base 10`

Binary is similar, but uses powers of 2 rather than powers of 10.

So: `101 => 1*2^2 + 0*2^1 + 1*2^0 => 1*4 + 0*2 + 1*1 => 4 + 1 => 5 base 10`.

Refer to the Exercism CoffeScript page for getting started with CoffeeScript.

In order to run the test, you can run the test file from the exercise directory:

``````jasmine-node --coffee .
``````

## Source

All of Computer Science http://www.wolframalpha.com/input/?i=binary&a=*C.binary-_*MathWorld-

## Submitting Incomplete Solutions

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

### binary_test.spec.coffee

``````Binary = require './binary'

describe 'binary', ->

it '1 is decimal 1', ->
expect(new Binary('1').toDecimal()).toEqual 1

xit '10 is decimal 2', ->
expect(new Binary('10').toDecimal()).toEqual 2

xit '11 is decimal 3', ->
expect(new Binary('11').toDecimal()).toEqual 3

xit '100 is decimal 4', ->
expect(new Binary('100').toDecimal()).toEqual 4

xit '1001 is decimal 9', ->
expect(new Binary('1001').toDecimal()).toEqual 9

xit '11010 is decimal 26', ->
expect(new Binary('11010').toDecimal()).toEqual 26

xit '10001101000 is decimal 1128', ->
expect(new Binary('10001101000').toDecimal()).toEqual 1128

xit 'carrot is decimal 0', ->
expect(new Binary('carrot').toDecimal()).toEqual 0

xit 'numeric but non-binary string is decimal 0', ->
expect(new Binary('42').toDecimal()).toEqual 0``````
``````module.exports = class Binary
constructor: (@str) ->
@invalid = (/^01/).test(@str)
@reverse_str = @str.split("").reverse().join("")

toDecimal: ->
return 0 if @invalid

result = 0
for i in [0..@reverse_str.length - 1]
result += 2 ** i if @reverse_str[i] == "1"

result``````