input: Write a function to convert a number into its binary format. Return the binary representation as a string. If the input number is 0, return "0".
  assert convert_to_binary(0)=='0'
  assert convert_to_binary(10)=='1010'
  assert convert_to_binary(7)=='111'
  assert convert_to_binary(16)=='10000'
  assert convert_to_binary(5)=='101'
output: def convert_to_binary(num):
      if num == 0:
          return "0"
      binary_str = ""
      while num > 0:
          binary_str = str(num % 2) + binary_str
          num = num // 2
      return binary_str