input: Write a function to convert an HTML string to plain text without using any libraries. The function should iterate through the input string, ignoring characters that are part of HTML tags and collecting only the plain text characters.
  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("<p>Hello, <b>world</b>!</p>")=='Hello, world!'
  assert html_to_text("<h1>Title</h1>")=='Title'
  assert html_to_text("<div>Content</div>")=='Content'
  assert html_to_text("No tags here")=='No tags here'
  assert html_to_text("")==''
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