CODEWITHSUNDEEP
ruby-on-railsruby
Sergey Chechaev
Sergey Chechaev

Reputation: 570

Convert integer to binary string, padded with leading zeros

I want to create new method Integer#to_bin that convert decimal to a binary string. The argument of #to_bin is the number of digits. The result should be padded with leading zeros to make it have that many digits.

Example:

1.to_bin(4)
#=> "0001"
1.to_bin(3)
#=> "001"
1.to_bin(2)
#=> "01"
7.to_bin(1)
#=> nil
7.to_bin
#=> "111"
etс.

What I've tried:

class Integer

    def to_bin(number=nil)
        if number == nil
          return self.to_s(2)
        else 
          s = self.to_s(2).size
          e = number-s
          one = '0'
          two = '00'
          three = '000'

        if e==one.size
          one+self.to_s(2)
        elsif e==two.size
          two+self.to_s(2)
        elsif e==three.size
          three+self.to_s(2)
        end
        end
    end
end

How do I convert an integer to a binary string padded with leading zeros?

Upvotes: 3

Views: 7157

Answers (2)

the Tin Man
the Tin Man

Reputation: 160551

The appropriate way to do this is to use Kernel's sprintf formatting:

'%03b' % 1 # => "001"
'%03b' % 2 # => "010"
'%03b' % 7 # => "111"

'%08b' % 1 # => "00000001"
'%08b' % 2 # => "00000010"
'%08b' % 7 # => "00000111"

But wait, there's more!:

'%0*b' % [3, 1] # => "001"
'%0*b' % [3, 2] # => "010"
'%0*b' % [3, 7] # => "111"

'%0*b' % [8, 1] # => "00000001"
'%0*b' % [8, 2] # => "00000010"
'%0*b' % [8, 7] # => "00000111"

So defining a method to extend Fixnum or Integer is easy and cleanly done:

class Integer
  def to_bin(width)
    '%0*b' % [width, self]
  end
end

1.to_bin(8) # => "00000001"
0x55.to_bin(8) # => "01010101"
0xaaa.to_bin(16) # => "0000101010101010"

Upvotes: 35

Chris Heald
Chris Heald

Reputation: 62648

Ruby already has a built-in mechanism to convert a number to binary: #to_s accepts a base to convert to.

30.to_s(2) # => "11110"

If you want to left-pad it with zeroes:

30.to_s(2).rjust(10, "0") => "0000011110"

You could extend this into a little method that combines the two:

class Fixnum
  def to_bin(width = 1)
    to_s(2).rjust(width, "0")
  end
end

> 1234.to_bin
=> "10011010010"
> 1234.to_bin(20)
=> "00000000010011010010"

Upvotes: 16

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