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

# JackRanGitHub's solution

## to Binary in the PHP Track

Published at Sep 10 2020 · 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.

## 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

1. Go to the root of your PHP exercise directory, which is `<EXERCISM_WORKSPACE>/php`. To find the Exercism workspace run

`````` % exercism debug | grep Workspace
``````
2. Get PHPUnit if you don't have it already.

`````` % wget --no-check-certificate https://phar.phpunit.de/phpunit.phar
% chmod +x phpunit.phar
``````
3. Execute the tests:

`````` % ./phpunit.phar binary/binary_test.php
``````

## 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.php

``````<?php

class BinaryTest extends PHPUnit\Framework\TestCase
{
public static function setUpBeforeClass() : void
{
require_once 'binary.php';
}

public function testItParsesBinary0ToDecimal0() : void
{
\$this->assertEquals(0, parse_binary('0'));
}

public function testItParsesBinary1ToDecimal1() : void
{
\$this->assertEquals(1, parse_binary('1'));
}

public function testItParsesDigits() : void
{
\$this->assertEquals(2, parse_binary('10'));
\$this->assertEquals(3, parse_binary('11'));
\$this->assertEquals(4, parse_binary('100'));
\$this->assertEquals(9, parse_binary('1001'));
}

public function testItParsesHundreds() : void
{
\$this->assertEquals(128, parse_binary('10000000'));
\$this->assertEquals(315, parse_binary('100111011'));
\$this->assertEquals(800, parse_binary('1100100000'));
\$this->assertEquals(999, parse_binary('1111100111'));
}

public function testItParsesMaxInt() : void
{
\$this->assertEquals(
9223372036854775807,
parse_binary('111111111111111111111111111111111111111111111111111111111111111')
);
}

{
\$this->assertEquals(1, parse_binary('01'));
\$this->assertEquals(2, parse_binary('0010'));
\$this->assertEquals(3, parse_binary('00011'));
}

/**
* @dataProvider invalidValues
*/
public function testItOnlyAcceptsStringsContainingZerosAndOnes(\$value) : void
{
\$this->expectException(InvalidArgumentException::class);

parse_binary(\$value);
}

public function invalidValues() : array
{
return [
['2'], ['12345'], ['a'], ['0abcdef'],
];
}
}``````
``````<?php

function parse_binary(\$binary)
{
\$output = 0;
\$binaryLength = strlen(\$binary);
for (\$i = 0; \$i < \$binaryLength; \$i ++) {
if (!is_numeric(\$binary[\$i]) || \$binary[\$i] > 1) {
throw new InvalidArgumentException();
}
\$exponent = \$binaryLength - \$i - 1;
\$output = bcadd(\$output, bcmul(\$binary[\$i], bcpow(2, \$exponent)));
}
return (int) \$output;
}``````