Array of linked lists in C++

Question

Some code for context:

class WordTable
{
public:
 WordTable();
 ~WordTable();

 List* GetListByAlphaKey(char key);
 void AddListByKey(char key);
 bool ListExists(char key);
 bool WordExists(string word);
 void AddWord(string word);
 void IncrementWordOccurances(string word);
 void Print();
private:     
    List *_listArray[33];
    int _GetIndexByKey(char key);
};



class TableBuilder
{
public:
 TableBuilder();
 ~TableBuilder();
 void AnalyzeStream(fstream &inputStream);        
    void PrintResults();
private:
    void _AnalyzeCursor(string data);
    bool _WordIsValid(string data);
    WordTable* _WordTable;        
};

struct Element {
public:
   string Word;
   int Occurances;
   Element* Next;
};



class List
{
public:
 List();
 ~List();

 Element* AddElement(string word);  
 void DeleteElement(Element* element);  
 void Print();  
 void Delete();
 Element* First;
 bool WordExists(string word);
 void IncrementWordOccurances(string word);  
private:
 void _PrintElementDetails(Element* element);


};

Requirements
I must analyze text, building array of linked lists (where array contains list for each letter; list contains every word found in text), then print out results.

Problem I can`t initialize array of lists in WordTable.cpp. I know that i've misunderstood something, but i got no ideas and time. Anyone?

P.s. Yeah, that's a homework. STOP giving me advices about best practices, please... :)

Answer 1

An initialization for _listArray would look like this:

WordTable::WordTable() {
  for (int i=0; i<33; i++)
    _listArray[i] = new List();
}

You don't really say what exactly the problem is so I'm not sure if this helps...

Answer 2

It's because you're creating an array of pointers to lists. Either change it to List _listArray[33]; or initialize it like so:

for ( int i = 0; i < 33; ++i ) {
    _listArray[i] = new List();
}

// and to access methods
_listArray[i]->AddElement( "word" );

Answer 3

It appears you are optimizing your linked lists by having an array of them, one for each first letter of the word. Don't do that.

Use std::map. Where the string is the word and the int is your count.

EDIT: If you ignore my advice... As has been pointed out your _listArray is actually an array of pointers, not an array of objects. I think you wanted an array of objects. Since the array is fixed length, and List has a default constructor, the simplest way to do that is to just say

List _listArray[33];

If you want dynamic allocation, you could do this instead:

List* _listArray;

And in the constructor:

_listArray = new List[33];

And in the destructor:

delete[] _listArray;

Answer 4

What you describe does not match your code.

List *_listArray[33]; does not define an array of linked lists. It defines an array of pointers to List.

Answer 5

Please don't reinvent the wheel (again) Use std::list it works correctly, is safer, is standard.

Second : you have design problems : element attribute in list is public, but you have a private method ???.