How to reverse the order of words in a sentence but also each word

This is a common trick which can be done using pointers in C/C++, but the principle is the same for other languages: first reverse the whole sentence, disregarding the words, then reverse each word by itself (words are separated by whitespace).

The method to reverse a string is easy:

   1:  void reverseWord(char*& word, int len) {

   2:      for (int i = 0; i < len / 2; i++) {

   3:          char temp = word[i];

   4:          char temp2 = word[len - i - 1];

   5:          *(word +i) = temp2;

   6:          word[len - i - 1] = temp;

   7:      }

   8:  }

So we could use the above function to reverse the order of words in a sentence and also the letters in each word:

   1:      string s = "This is a test run";

   2:      char* str = const_cast<char*>(s.c_str());

   3:      int size = s.size();

   4:      cout << "Initial string is: ";

   5:      for (int i = 0; i < size; i++)

   6:          cout << str[i];

   7:      cout << endl;

   8:      reverseWord(str, size);

   9:      cout << "Whole string reversed is: ";

  10:      for (int i = 0; i < size; i++)

  11:          cout << str[i];

  12:      cout << endl;

  13:      // do stuff here

  14:      int k = 0;

  15:      int start = 0;

  16:      char* tmp = str;

  17:      while (k <= size) {

  18:          if (str[k] == ' ' || str[k] == '\0') {

  19:              reverseWord(tmp, k - start);

  20:              tmp = str + k + 1;

  21:              start = k + 1;

  22:          }

  23:          ++k;

  24:      }

  25:      //

  26:      cout << "After processing, string is: ";

  27:      for (int i = 0; i < size; i++)

  28:          cout << str[i];

  29:      cout << endl;

The complexity is... O(n) ?