input: Write a function to convert a given number into its binary format. If the number is zero, return '0'.
  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(0) == '0'
  assert convert_to_binary(5) == '101'
  assert convert_to_binary(10) == '1010'
  assert convert_to_binary(16) == '10000'
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