Error "System.AccessViolationException" show binary tree after cut visualc++ - c++

Question

I have a problem with this Binary Search Tree.
After that i cut a leave, if I try to show the tree VisualStudio answer me this message
An unhandled exception of type 'System.AccessViolationException' occurred in ABR1.exe
Additional information: Attempted to read or write protected memory. This is often an indication that other memory is corrupt.
It's more that 3 days that i try to understand could someone help me???
// ABR1.cpp : main project file.
#include "stdafx.h"
#include <iostream>
using namespace System;
using namespace std;
template <class T>
class ABR{
private:
struct Leaf{
T value;
struct Leaf *DX; //
struct Leaf *SX; //
};
Leaf *root;
public:
//constructors
ABR() { root = NULL; }
//destructor
//~ABR();
void appendLeaf(T);
bool cutLeaf(T);
bool isInTree(T) const;
Leaf* findLeaf(T) const;
void showTreeInOrder() const { showTreeInOrder(root); }
void showTreeInOrder(Leaf *) const;
void showTreePreOrder() const { showTreePreOrder(root); }
void showTreePreOrder(Leaf *) const;
};
template <class T>
void ABR<T>::appendLeaf(T newValue){
if (isInTree(newValue)){
cout << "The value is just present..." << endl;
return;
}
Leaf *newLeaf; // To point to a new leaf
Leaf *ptrLeaf; // To move in the tree
// Allocate the necessary memory
newLeaf = new Leaf; //generate the new leaf
newLeaf-> value = newValue;
newLeaf-> DX = NULL;
newLeaf-> SX = NULL;
if(!root) //if is the first leaf
root = newLeaf;
else{
ptrLeaf = root;
//cout<<ptrLeaf->value<<ptrLeaf->SX<<ptrLeaf->DX<<endl;
while (ptrLeaf != NULL){
//cout << ptrLeaf->value <<"\t";
if (ptrLeaf->value < newValue){
if (ptrLeaf->DX == NULL){
ptrLeaf->DX = newLeaf;
return;
}
else
ptrLeaf = ptrLeaf->DX;
}
else{
if(ptrLeaf->SX == NULL){
ptrLeaf->SX = newLeaf;
return;
}
else
ptrLeaf = ptrLeaf->SX;
}
}
}
}
template <class T>
bool ABR<T>::isInTree(T toFind) const{
Leaf *ptrLeaf;
ptrLeaf = root;
while (ptrLeaf){
if (ptrLeaf->value == toFind)
return true;
else{
if (ptrLeaf->value < toFind)
ptrLeaf = ptrLeaf->DX;
else
ptrLeaf = ptrLeaf->SX;
}
}
return false;
}
template <class T>
typename ABR<T>::Leaf * ABR<T>::findLeaf(T toFind) const
{
Leaf *ptr;
ptr = root;
while(ptr != NULL)
{
//cout << ptr->value << "#" << endl;
if (toFind == ptr->value){
//cout << "Trovato";
return ptr;
}
else if (ptr->value < toFind)
ptr = ptr->DX;
else
ptr = ptr->SX;
} cout << "Element don't find" << endl;
return NULL;
}
template <class T>
void ABR<T>::showTreeInOrder(Leaf *ptr) const
{
if(ptr != NULL)
{
showTreeInOrder(ptr->SX);
cout << ptr->value << endl;
showTreeInOrder(ptr->DX);
}
}
template <class T>
void ABR<T>::showTreePreOrder(Leaf *ptr) const
{
if(ptr != NULL)
{
showTreePreOrder(ptr->DX);
cout << ptr->value << endl;
showTreePreOrder(ptr->SX);
}
}
template <class T>
bool ABR<T>::cutLeaf(T toCut)
{
Leaf *Leafptr, *tempLeafptr;
Leafptr = findLeaf(toCut);
if (Leafptr == NULL)
{
cout << "The element is not present..." << endl;
return false;
}
else if (Leafptr->DX == NULL)
{
tempLeafptr = Leafptr;
Leafptr = Leafptr->SX;
delete tempLeafptr;
return true;
}
else if (Leafptr->SX == NULL)
{
tempLeafptr = Leafptr;
Leafptr = Leafptr->DX;
delete tempLeafptr;
return true;
}
else
{
tempLeafptr = Leafptr->DX;
while (tempLeafptr->SX)
tempLeafptr = tempLeafptr->SX;
tempLeafptr->DX = Leafptr->SX;
tempLeafptr = Leafptr;
Leafptr = Leafptr->DX;
delete tempLeafptr;
return true;
}
}
int main(){
ABR<int> albero;
for(int a = 0.0; a < 100.0; a+= 3)
albero.appendLeaf(a);
albero.appendLeaf(1000);
albero.appendLeaf(1001);
albero.showTreePreOrder();
int b = 75;
albero.cutLeaf(b);
albero.showTreePreOrder(); //ERROR
//albero.showTreeInOrder();//SAME ERROR
system("PAUSE");
return 0;
}

Answer 1

You're recursing in showTreePreOrder and encountering a stack overflow. Running it in the debugger told me this in under one minute.
EDIT:
Your problem is in this section of cutLeaf(). First, you're assuming Leafptr->SX isn't null and you're deleting it, but it is null for the last leaf. Second, when you delete the leaf you don't set its parent's DX pointer to null. Therefore, when you traverse the list, you traverse into leaves that have been freed.
else if (Leafptr->DX == NULL)
{
tempLeafptr = Leafptr;
Leafptr = Leafptr->SX;
delete tempLeafptr;
return true;
}
The same problems exist in the else clause.