C++ linked lists problem

[hobokook]

Hi,
I have an assignment where I have to implement a singly linked list of integers. Can you look at my pop front function below to see if it would work. I think it works, but I get this weird error whenever I test it. Also, how would I do my push back fucntion to add a number to the back end of the list. I know all linked lists end in NULL, but how would I write that out?

Thanks

My file definition:

#ifndef INTLIST_H_INCLUDED
#define INTLIST_H_INCLUDED

#ifndef NULL
#define NULL 0
#endif

class IntNode
{
  public:
    int data;
    IntNode *next;

    IntNode(int data)
    : data(data), next(NULL)
    {}
};

class IntList
{
    private:
        IntNode *head;

    public:
        IntList();
        ~IntList();
        unsigned int get_size() const;
        void print() const;
        const int &at(unsigned int index) const;
        int &at(unsigned int index);
        void push_front(int data);
        void push_back(int data);
        void pop_front();
        void select_sort();
        void insert_sorted(int value);
        void erase(unsigned int position);
        void remove_duplicates();
};
#endif // INTLIST_H_INCLUDED

My implementation:

#include <iostream>
#include "IntList.h"
using namespace std;

IntList::IntList()
:  head(NULL)
{}

IntList::~IntList()
{}

unsigned int IntList::get_size()const
{
    unsigned int count = 0;
    for(IntNode *i=head;i;i->next)
    {
        ++count;
    }
    return count;
}

void IntList::print()const
{
    for(IntNode *i = head;i;i=i->next)
    {
        cout << i->data << " ";
    }
}


//insert front end
void IntList::push_front(int data)
{
    IntNode *new_node = new IntNode(data);

    new_node->next = head; //or other way around not sure
    head = new_node;

    delete new_node;
}

// insert back end
void IntList::push_back(int data)
{
    IntNode *new_node = new IntNode(data);

}

void IntList::pop_front()
{
    if(!head)
        return;

    IntNode *del = head;
    head = head->next;

    delete del;
}

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