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

# jagodakosinska's solution

## to Binary in the PHP Track

Published at Jul 01 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)
{

\$bin_len = strlen(\$binary) - 1;
\$a = 0;
\$j = \$bin_len;
invalidValues(\$binary);
for (\$i = 0; \$i <= \$bin_len; \$i++) {
\$a += \$binary[\$i] * pow(2, \$j);
\$j--;
}

return \$a;
}

function invalidValues(\$binary)
{
\$arr = str_split(\$binary, 1);
foreach (\$arr as \$v) {
if (\$v > 2 || !is_numeric(\$v)) throw new InvalidArgumentException('invalid argument');
}
}``````

### What can you learn from this solution?

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?