input: Write a python function to convert an integer to its binary representation without using built-in functions.
  assert int_to_binary(5) == '101'
  assert int_to_binary(10) == '1010'
  assert int_to_binary(0) == '0'
  assert int_to_binary(255) == '11111111'
output: def int_to_binary(n):
      if n == 0:
          return '0'
      result = ''
      while n > 0:
          result = str(n % 2) + result
          n = n // 2
      return result