input: Write a function to convert a given string to Pig Latin.
  assert convert_string_to_pig_latin("hello world") == "ellohay orldway"
  assert convert_string_to_pig_latin("apple pie") == "appleway iepay"
  assert convert_string_to_pig_latin("python programming") == "ythonpay rogrammingpay"
output: def convert_string_to_pig_latin(s):
      def pig_latin_word(word):
          vowels = 'aeiouAEIOU'
          if word[0] in vowels:
              return word + 'way'
          else:
              return word[1:] + word[0] + 'ay'
      
      return ' '.join(pig_latin_word(word) for word in s.split())