countw3.cc From Astrachan, pp 270-272
-------------------------------------
#include <iostream.h>
#include <fstream.h>
#include "CPstring.h"
#include "prompt.h"

// count words in stream bound to text file
// uses a WordStreamIterator class to hide I/O details

class WordStreamIterator
{
  public:
    
    WordStreamIterator();
    void Open(string name);           // bind stream to specific text file
    void First();                     // initialize iterator
    string Current();                 // returns current word
    bool IsDone();                    // true if iterator is done
    void Next();                      // advance to next word

  private:
    
    string myWord;                    // the current word
    bool myDone;                      // true if no more words
    ifstream myInput;                 // the stream to read from
};

WordStreamIterator::WordStreamIterator()
// postcondition: iterator is initialized, IsDone() == true     
{
    myWord = "";
    myDone = true;              // First() must be called 
}

void WordStreamIterator::Open(string name)
{
    myInput.open(name);
}

void WordStreamIterator::First()
// postcondition: first word read from stream myInput
{
    myInput.seekg(0);                   // back to beginning
    myInput.clear();                    // clear the stream
    myDone = ! (myInput >> myWord);     // read first word, set state
}


string WordStreamIterator::Current()
// precondition: IsDone() == false
// postcondition: returns current word     
{
    return myWord;
}

bool WordStreamIterator::IsDone()
// postcondition: returns true if no words left in stream
//                (all words have been read) otherwise returns false
{
    return myDone;
}

void WordStreamIterator::Next()
// precondition: ! IsDone()     
// postcondition: next word from stream myInput read     
{
    if (! IsDone())
    {
        myDone = ! (myInput >> myWord);
    }
}

int main()
{
    string word;
    int numWords = 0;                  // initially, no words
    WordStreamIterator iter;

    iter.Open(PromptString("enter name of file: "));
    
    for(iter.First(); ! iter.IsDone(); iter.Next())
    {
        numWords++;
    }
    cout << "number of words read = " << numWords << endl;
    
    return 0;
}