ðŸŽ‰ Exercism Research is now launched. Help Exercism, help science and have some fun at research.exercism.io ðŸŽ‰

# amscotti's solution

## to Binary in the Nim Track

Published at Jul 23 2018 · 0 comments
Instructions
Test suite
Solution

#### Note:

This exercise has changed since this solution 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`.

## Running the tests

To compile and run the tests, just run the following in your exercise directory:

``````\$ nim c -r binary_test.nim
``````

## Submitting Exercises

Note that, when trying to submit an exercise, make sure the solution is in the `\$EXERCISM_WORKSPACE/nim/binary` directory.

You can find your Exercism workspace by running `exercism debug` and looking for the line that starts with `Exercises Directory`.

For more detailed information about running tests, code style and linting, please see the help page.

## 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.nim

``````import unittest
import binary

suite "Binary":

test "binary 0 is decimal 0":
check binary("0") == 0

test "binary 1 is decimal 1":
check binary("1") == 1

test "binary 10 is decimal 2":
check binary("10") == 2

test "binary 11 is decimal 3":
check binary("11") == 3

test "binary 100 is decimal 4":
check binary("100") == 4

test "binary 1001 is decimal 9":
check binary("1001") == 9

test "binary 11010 is decimal 26":
check binary("11010") == 26

test "binary 10001101000 is decimal 1128":
check binary("10001101000") == 1128

check binary("000011111") == 31

test "2 is not a valid binary digit":
expect(ValueError):

test "a number containing a non-binary digit is invalid":
expect(ValueError):

test "a number with trailing non-binary characters is invalid":
expect(ValueError):

test "a number with leading non-binary characters is invalid":
expect(ValueError):

test "a number with internal non-binary characters is invalid":
expect(ValueError):

test "a number and a word whitespace spearated is invalid":
expect(ValueError):
``````import
algorithm, math, strutils

proc binary*(input: string): int =
if not input.allCharsInSet({'0', '1'}):
raise newException(ValueError, "Input not only 0s and 1s")

for idx, i in reversed(input):
if i == '1':
result = result + pow(2, idx.toFloat).toInt``````