Ruby Decimal to Binary Conversion – Loops, Recursion & Bitwise Methods

What Are We Solving?

In this guide, we’ll explore how to convert a decimal number into binary using Ruby, covering various techniques — from manual logic to built-in utilities.

Each approach will demonstrate a slightly different programming style so you can see how Ruby makes such logic clean and expressive.

Use Cases

• Learning how number systems work at the code level.

• Building console-based binary converters.

• Writing Ruby scripts that deal with binary data formats.

• Technical interview preparation for base conversion problems.

Conversion Using While Loop and String Manipulation

# Convert decimal to binary using a while loop
def binary_with_loop(number)
  return "0" if number == 0
  binary = ""
  while number > 0
    binary = (number % 2).to_s + binary
    number /= 2
  end
  binary
end

puts "Binary of 45: #{binary_with_loop(45)}"

Explanation

• We divide the number repeatedly by 2.

• Each remainder is prepended to the binary result.

• Stops when the number becomes 0.

Output

Conversion Using Recursion

# Recursive approach to convert decimal to binary
def binary_recursive(number)
  return "" if number == 0
  binary_recursive(number / 2) + (number % 2).to_s
end

result = binary_recursive(22)
puts "Binary of 22: #{result.empty? ? '0' : result}"

Explanation

• The function divides the number recursively.

• Each bit is collected as the stack unwinds.

• Base case: if number is 0, return empty string.

Output

Conversion Using Bitwise Operators

# Convert decimal to binary using bitwise shifting
def binary_with_bitwise(number)
  return "0" if number == 0
  result = ""
  started = false

  (31).downto(0) do |i|
    bit = (number >> i) & 1
    started ||= bit == 1
    result += bit.to_s if started
  end

  result
end

puts "Binary of 18: #{binary_with_bitwise(18)}"

Explanation

• Right shift the number bit-by-bit.

• Extract each bit using AND operation.

• Skip all leading zeros until first 1 appears.

Output

Instant Conversion Using Ruby’s Built-in Method

# Built-in method to convert decimal to binary
number = 12
puts "Binary of #{number}: #{number.to_s(2)}"

Explanation

• .to_s(2) converts the integer to base-2 (binary) string format.

• Easiest and fastest method for one-liners.

Output

Final Thoughts

Ruby provides both manual control and built-in ease when it comes to binary conversion. Whether you’re preparing for interviews, building educational tools, or just exploring how numbers work, these 4 techniques offer a well-rounded learning path.