decimal_to_binary.rb

def dec2bin(number)
    number = Integer(number)
    if(number == 0) then 0 end
        
    ret_bin = ""
    while(number != 0)
        ret_bin = String(number % 2) + ret_bin
        number = number / 2
    end
    ret_bin
end

# Integer("0b#{dec2bin 5}") will convert back to decimal.