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

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`

.

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

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

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`

.

These guides should help you,

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.

```
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
test "binary ignores leading zeros":
check binary("000011111") == 31
test "2 is not a valid binary digit":
expect(ValueError):
discard binary("2")
test "a number containing a non-binary digit is invalid":
expect(ValueError):
discard binary("01201")
test "a number with trailing non-binary characters is invalid":
expect(ValueError):
discard binary("10nope")
test "a number with leading non-binary characters is invalid":
expect(ValueError):
discard binary("nope10")
test "a number with internal non-binary characters is invalid":
expect(ValueError):
discard binary("10nope10")
test "a number and a word whitespace spearated is invalid":
expect(ValueError):
discard binary("001 nope")
```

```
proc binary*(binary:string): int =
for ch in binary:
if ch != '0' and ch != '1':
raise newException(ValueError, "Not valid binary")
result = result * 2 + (if ch == '1': 1 else: 0)
```

A huge amount can be learned from reading other peopleâ€™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?

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