input: Write a function that converts a given string to its lowercase version. The function should iterate through each character in the string, convert it to lowercase, and then return the new lowercase 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")=="python"
  assert str_to_lower("UPPERCASE")=="uppercase"
  assert str_to_lower("123 ABC")=="123 abc"
output: def str_to_lower(string):
      new_string = ""
  
      for char in string:
          new_string += char.lower()
  
      return new_string