How to convert decimal value to binary value?

Questions / Help
1

I want to convert “3” to “11”, and then “11” to “00000011” in elixir.
But I don’t know any ways to do it.

Help me!

2

When I don’t know how to do something in Elixir, the first place I look is the module that has code related to the kind of data I’m trying to deal with. In this case, you’re trying to turn a String into an integer, and then represent that integer in a particular base.

Turning a string into an integer can be accomplished with a function found in this module: https://hexdocs.pm/elixir/String.html

And turning an integer into the digits of a specific base can be found with a function in this module: https://hexdocs.pm/elixir/Integer.html

Give it a shot! We’ll be here if you have further questions.

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3

As an alternative to @benwilson512 's method, sometimes I just fire up an iex and h SomeModule.<tab> or something alike, and search for the function that could work. If none is found, I’ll try h Kernel.<tab>.

For example, for the last step in your problem, I’d h String.<tab>, and fortunately, I can find pad_leading/2 and pad_leading/3 in the function list, then I h String.pad_leading to view their documentation.

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4

Just format it properly - List.to_string(:io_lib.format("~8.2B", [3]))

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5

You can break this down into 3 easy steps using the modules that @benwilson512 recommends.

  1. Convert string to integer String.to_integer("3")

  2. Get binary value of integer Integer.to_string(3, 2)

  3. Pad binary string with zeros String.pad_leading("11", 8, "0")

You can write the code with guard clauses to handle strings or integers.

  def decimal_to_binary(decimal) when is_binary(decimal) do
    decimal
    |> String.to_integer()
    |> decimal_to_binary()
  end

  def decimal_to_binary(decimal) when is_integer(decimal) do
    decimal
    |> Integer.to_string(2)
    |> String.pad_leading(8, "0")
  end
6 Likes
6

Still IMHO overcomplicated:

def decimal_to_binary(str) when is_binary(str) do
  decimal
  |> String.to_integer()
  |> decimal_to_binary()
end

def decimal_to_binary(num) when is_integer(num),
  do: List.to_string(:io_lib.format("~8.2B", [num]))
1 Like
7

This gives leading whitespaces, not zeroes. Do you know if there’s a modifier to make it do zeroes?

3 Likes
8

Oh yeah, it should be "~8.2.0B"

6 Likes
9

Thank you!
All suggestions helped me!

10

None of the “written code” solutions here work for numbers greater than 255.

I think this solution works for all (positive) numbers:

  def decimal_to_binary(str) when is_binary(str) do
    str
    |> String.to_integer()
    |> decimal_to_binary()
  end

  def decimal_to_binary(num) when is_integer(num) do
    binary_string = :erlang.integer_to_binary(num, 2)
    binary_string_length = String.length(binary_string)
    desired_string_length = binary_string_length + (8 - rem(binary_string_length, 8))
    String.pad_leading(binary_string, desired_string_length, "0")
  end

It could probably be neater but at least it works for numbers larger than 255.

Any improvements are very welcome!

1 Like