input: Write a function to convert a given string to its lowercase version. The function should iterate through each character in the string, convert it to lowercase using the lower() method, and return the new string with all characters in lowercase. If the input string is empty, it should return an empty string.
  
  def str_to_lower(string):
      new_string = ""
  
      for char in string:
          new_string += char.lower()
  
      return new_string
  
  assert str_to_lower("Hello World") == "hello world"
  assert str_to_lower("PYTHON IS FUN") == "python is fun"
  assert str_to_lower("123abC") == "123abc"
  assert str_to_lower("") == ""
output: def str_to_lower(string):
      new_string = ""
  
      for char in string:
          new_string += char.lower()
  
      return new_string