input: Write a function to search for matches between a user input string and a list of predefined strings. If a match is found, return "String matches"; otherwise, return "String doesn't match". The function should use regular expressions to perform the search.
  assert search_string(["First","Second","Third"], "Second") == "String matches"
  assert search_string(["First","Second","Third"], "Fourth") == "String doesn't match"
  assert search_string([], "First") == "String doesn't match"
  assert search_string(["First","Second","Third"], "rst") == "String matches"
output: import re
  
  def search_string(predefined_strings, user_input):
      for string in predefined_strings:
          if re.search(user_input, string):
              return "String matches"
      return "String doesn't match"