input: Write a function to convert an HTML string to plain text without using any libraries. The function should remove all HTML tags and return the remaining plain text.
  def html_to_text(html_string):
      output = ''
      in_tag = False
      for char in html_string:
          if char == '<':
              in_tag = True
          elif char == '>':
              in_tag = False
          elif in_tag == False:
              output += char
      return output
  
  assert html_to_text("Hello, <b>world</b>!") == "Hello, world!", "Test case 1 failed"
  assert html_to_text("This is an <a href='example.com'>example</a>.") == "This is an example.", "Test case 2 failed"
  assert html_to_text("<p>Paragraph here</p>") == "Paragraph here", "Test case 3 failed"
  assert html_to_text("") == "", "Test case 4 failed"
  assert html_to_text("<br>") == "", "Test case 5 failed"
output: def html_to_text(html_string):
      output = ''
      in_tag = False
      for char in html_string:
          if char == '<':
              in_tag = True
          elif char == '>':
              in_tag = False
          elif in_tag == False:
              output += char
      return output