input: Write a function to convert a number into binary format. If the number is 0, return 0. Otherwise, return the binary representation of the number as a string. 
  
  def convert_to_binary(num):
      if num == 0:
          return 0
      binary = ''
      while num != 0:
          remainder = num % 2
          binary = str(remainder) + binary
          num = num // 2
      return binary
  
  assert convert_to_binary(10) == '1010'
  assert convert_to_binary(5) == '101'
  assert convert_to_binary(0) == 0
  assert convert_to_binary(15) == '1111'
output: def convert_to_binary(num):
      if num == 0:
          return 0
      binary = ''
      while num != 0:
          remainder = num % 2
          binary = str(remainder) + binary
          num = num // 2
      return binary