Question

My program is calling a member function that performs an insertion into a binary search tree with a pointer passed by reference (so that the value of the pointer is changed). However when I attempt to insert a second node into the tree the program crashes. I am assuming that this has to do with a bad pointer.

The only part of this assignment that can be changed is the implementation of the member functions and not there declaration.

Any help would be appreciated.

 //Header file
using namespace std;

struct PersonRec
{
    char name[20];
    int bribe;
    PersonRec* leftLink;
    PersonRec* rightLink;
};


class CTree
{

private:
    PersonRec *tree;
    bool IsEmpty();
    void AddItem( PersonRec*&, PersonRec*);
    void DisplayTree(PersonRec*);

public:
    CTree();
    //~CTree();
    void Add();
    void View();

};

//Implementation file

#include <iostream>
#include <string>

using namespace std;

#include "ctree.h"

CTree::CTree()
{
    tree = NULL;
}

//PersonList::~MyTree()
//{
//
//}


bool CTree::IsEmpty()
{
    if(tree == NULL) 
    {
        return true;
    }
    else
    {
        return false;
    }
}

void CTree::Add()
{
    PersonRec* newPerson = new PersonRec();
    cout << "Enter the person's name: ";
    std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
    cin.getline(newPerson->name, 20);
    cout << "Enter the person's contribution: ";
    cin >> newPerson->bribe;


    newPerson->leftLink = NULL;
    newPerson->rightLink = NULL;

    AddItem(tree, newPerson);
}

void CTree::View()
{
    if (IsEmpty())
    {
        cout<<"The list is empy";
    }
    else
    {
        DisplayTree(tree);

    }

};

void CTree::AddItem( PersonRec*& ptr, PersonRec* newPer )
{
        if (tree == NULL)
        {
            ptr = newPer;
        }
        else if ( newPer->bribe < ptr->bribe)
            AddItem(ptr->leftLink, newPer); 
        else
            AddItem(ptr->rightLink, newPer); 
}
void CTree::DisplayTree(PersonRec* ptr)
{
    if (ptr == NULL)
                    return;
    DisplayTree(ptr->rightLink);
    cout<<ptr->name<<" "<<"$"<<ptr->bribe <<endl;
    DisplayTree(ptr->leftLink); 
}


//Driver file
#include <iostream>

using namespace std;
#include <cstdlib>
#include "ctree.h"

int displayMenu (void);
void processChoice(int, CTree&);

int main (void)
{
int num;
CTree ct;
do 
{
num = displayMenu();
if (num != 3)
processChoice(num, ct);
} while (num != 3);
return 0;
}

int displayMenu (void)
{
int choice;
cout << "\nMenu\n";
cout << "==============================\n\n";
cout << "1. Add student to waiting list\n";
cout << "2. View waiting list\n";
cout << "3. Exit program\n\n";
cout << "Please enter choice: ";
cin >> choice;
return choice;
}

void processChoice(int choice, CTree& myTree)
{
   switch (choice)
   {
      case 1: myTree.Add (); break;
      case 2: myTree.View (); break;
   } 
}

Answer 1

In CTree::AddItem, your condition is wrong:

    if (tree == NULL)
    {
        ptr = newPer;
    }

should be

    if (ptr == NULL)
    {
        ptr = newPer;
    }

When you call AddItem(ptr->rightLink, newPer);, newPer is the new node, but either of the descendants of the current root can be NULL, so that’s what you need to check for NULL and replace, not the new node.