input: Write a function to convert a decimal number into its binary format. The function should return a string representation of the binary number. If the input is 0, the function should return '0'. 
  
  def convert_to_binary(num):
      # check if the number is 0, if so return '0'
      if num == 0:
          return '0'
      
      # initialize an empty binary string
      binary = ''
      
      # loop through the number and get the remainder 
      # which is the bits of the 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(10) == '1010'
  assert convert_to_binary(7) == '111'
  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