input: Write a function to convert a number into its binary representation. If the number is zero, return zero as the binary representation.
  
  def convert_to_binary(num):
      if num == 0:
          return '0'
      binary = ''
      while num > 0:
          binary = str(num % 2) + binary
          num = num // 2
      return binary
  
  assert convert_to_binary(0)=='0'
  assert convert_to_binary(2)=='10'
  assert convert_to_binary(7)=='111'
  assert convert_to_binary(10)=='1010'
  assert convert_to_binary(32)=='100000'
output: def convert_to_binary(num):
      if num == 0:
          return '0'
      binary = ''
      while num > 0:
          binary = str(num % 2) + binary
          num = num // 2
      return binary