input: Write a function to convert a number into binary format. The function should return the binary representation in string form. If the number is zero, the function should 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
  
  # test the function 
  assert convert_to_binary(0) == "0"
  assert convert_to_binary(10) == "1010"
  assert convert_to_binary(255) == "11111111"
  assert convert_to_binary(-5) == "-101"
  assert convert_to_binary(256) == "100000000"
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