Linked List Crashes after all nodes are deleted - c++

Question

Our homework assignment wanted us to create a "Staque" (implements features of a stack and a queue) using a linked list. When entering even numbers in the list, they should go to the top of the list and odd numbers at the bottom. So if the values inserted are 8 1 4 6 7 9 it should output 6 4 8 1 7 9. Then you delete the top two even numbers and the bottom odd number which would give 8 1 7. Everything seems to work fine except when all the nodes are deleted so when you enter 3 or less values, the program crashes. At this time I have to turn in my assignment since it's due tonight but am just wondering how this can be resolved. Any help would be appreciated.
Here is my code:
Driver:
#include <iostream>
#include "Staq.h"
using namespace std;
int main()
{
Staq *std = new Staq();
int numofvals;
int i;
int x;
cout << "How many values in the staque?" << endl;
cin >> numofvals;
cout << numofvals << " values will be entered in the staque." << endl << endl;;
for(i=1; i<=numofvals; i++)
{
cout << "Enter value " << i << ":" << endl;
cin >> x;
std->AddNode(x);
}
cout << endl;
cout << "Staque:" << endl;
std->PrintList();
std->DeleteNode();
cout << "\nStaque after deletions:" << endl;
std->PrintList();
return 0;
}
.CPP:
#include <iostream>
using namespace std;
#include "Staq.h"
Staq::Staq()
{
head = NULL;
curr = NULL;
temp = NULL;
}
void Staq::AddNode(int addData)
{
nodePtr n = new node;
n->next = NULL;
n->data = addData;
if(addData % 2 == 0)
{
if(head == NULL)
{
head = n;
curr = n;
}
else
{
n->next = head;
head = n;
}
}
else
{
if(head == NULL)
{
head = n;
curr = n;
}
else
{
temp = head;
while(temp->next != NULL)
{
temp = temp->next;
}
temp->next = n;
}
}
}
void Staq::DeleteNode()
{
nodePtr temp2 = new node;
if(head->data %2 == 0)
{
temp = head;
head = head->next;
delete temp;
if(head->data %2 == 0)
{
temp = head;
head = head->next;
delete temp;
}
}
temp = head;
while(temp->next->next != NULL)
{
temp = temp->next;
}
if(temp->data %2 != 0)
{
temp2 = temp->next;
temp->next = NULL;
delete temp2;
}
}
void Staq::PrintList()
{
curr = head;
while(curr != NULL)
{
cout << curr->data << endl;
curr = curr->next;
}
}
Header:
#include <iostream>
using namespace std;
#ifndef STAQ_H
#define STAQ_H
class Staq
{
public:
Staq();
~Staq();
void AddNode(int addData);
void DeleteNode();
void PrintList();
private:
class node
{
public:
int data;
node* next;
};
typedef class node* nodePtr;
nodePtr head;
nodePtr curr;
nodePtr temp;
};
#endif

Answer 1

In DeleteNode, you attempt to access the first node's data, even if there isn't a node. Same goes for the second node.
while(temp->next->next) is dangerous because temp->next could be NULL therefore making temp->next->next an access to null pointer. I assume you meant temp->next. You might want to validate temp too.
Finally, although unrelated, temp2 = temp->next causes a memory leak because now no one points to the new node created at the beginning of DeleteNode.