Exercism v3 launches on Sept 1st 2021. Learn more! ๐๐๐

Published at Jul 13 2018
·
0 comments

Instructions

Test suite

Solution

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.

- 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
*n*th 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 .
```

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

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

```
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
```

A huge amount can be learned from reading other peopleโs 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?

Level up your programming skills with 3,450 exercises across 52 languages, and insightful discussion with our volunteer team of welcoming mentors.
Exercism is
**100% free forever**.

## Community comments