prog7_09.cpp

一本语言类编程书籍

// Program 7.9 Sorting strings using dynamic memory allocation
#include <iostream>
#include <string>
using std::cout;
using std::cin;
using std::endl;
using std::string;

int main() {
  string text;                                            // The string to be sorted
  const string separators = " ,.!:;\"\?\n\t";             // Word delimiters

  // Read the string to be searched from the keyboard
  cout << endl << "Enter a string terminated by #:" << endl;
  std::getline(cin, text, '#');

  // Count the words in the text
  size_t start = text.find_first_not_of(separators);      // Word start index
  size_t end = 0;                                         // End delimiter index
  int word_count = 0;                                     // Count of words stored

  while(start != string::npos) {
    end = text.find_first_of(separators, start + 1);
    if(end == string::npos)                               // Found a separator?
      end = text.length();                                // No, so set to last + 1
    word_count++;                                         // Increment count

    // Find the first character of the next word
    start = text.find_first_not_of(separators, end + 1);
  }

  // Allocate an array of pointers to strings in the free store
  string** pwords = new string*[word_count];

  start = text.find_first_not_of(separators);             // Word start index
  end = 0;                                                // End delimiter index
  int index = 0;                                          // Current array index

  while(start != string::npos) {
    end = text.find_first_of(separators, start + 1);
    if(end == string::npos)                               // Found a separator?
      end = text.length();                                // No, so set to last + 1
    pwords[index++] = new string(text.substr(start, end - start));  // Store the word
    
    // Find the first character of the next word
    start = text.find_first_not_of(separators, end + 1);
  }

  // Sort the words in ascending sequence using the array of pointers
  int lowest = 0;                                         // Index of lowest word

  for(int j = 0; j < word_count - 1 ; j++) {
    lowest = j;                                           // Set lowest 

    // Check current against all the following words
    for(int i = j + 1 ; i < word_count ; i++)
      if(*pwords[i] < *pwords[lowest])                    // Current is lower?
        lowest = i; 

	if(lowest != j) {               // Then swap pointers
      string* ptemp = pwords[j];                          // Save current
      pwords[j] = pwords[lowest];                         // Store lower in current
      pwords[lowest] = ptemp;                             // Restore current
    }
  }

  // Output up to six words to a line in groups starting with the same letter
  char ch = (*pwords[0])[0];                              // First letter of first word
  int words_in_line = 0;                                  // Words in a line count
  for(int i = 0; i < word_count ; i++) {
    if(ch != (*pwords[i])[0]) {                           // New first letter?
      cout << endl;                                       // Start a new line
      ch = (*pwords[i])[0];                               // Save the new first letter
      words_in_line = 0;                                  // Reset words in line count
    }
    cout << *pwords[i] << "  ";
    if(++words_in_line == 6) {                            // Every sixth word
      cout << endl;                                       // Start a new line
      words_in_line = 0;
    }
  }

  // Delete words from free store
    for(int i = 0 ; i < word_count ; i++)
      delete pwords[i];

  // Now delete the array of pointers
  delete [] pwords;

  cout << endl;
  return 0;
}