.exe has stopped working code blocks cpp - c++

Question

`Hello
I just wrote this code in Code Blocks and after building and running , it says that the programm has stopped working. I can't find what I have done wrong. I don't know if the problem is related to my code or is something that has to do with the compiler I am using or something else.
Please help
Library.h:
#ifndef LIBRARY_H
#define LIBRARY_H
#include <iostream>
#include <string>
using namespace std;
class Library
{
public:
struct book
{
string tittle;
int number;
struct book* next;
}* head, *tail, *ptr;
Library();
~Library();
book* searchName(book *, string);
void addNode(book *);
book *initNode(string s, int i);
void displayNode(book *ptr) const;
void displayList(book *ptr) const;
protected:
};
#endif
Library.cpp
#include "Library.h"
Library::Library() :
head(NULL), tail(NULL)
{
}
Library::~Library()
{
book *current, *temp;
current = head;
temp = head;
while (current != NULL)
{
current = current->next;
delete temp;
temp = current;
}
}
Library::book * Library::searchName(Library::book* ptr, string name)
{
while (name != ptr->tittle)
{
ptr = ptr->next;
if (ptr == NULL)
break;
}
return ptr;
}
void Library::addNode(book *newNode)
{
if (head == NULL)
{
head = newNode;
head = newNode;
}
tail->next = newNode;
newNode->next = NULL;
tail = newNode;
}
Library::book *Library::initNode(string s, int i)
{
book *ptr = new book;
if (ptr == NULL)
return static_cast<book *>(NULL);
else
{
ptr->tittle = s;
ptr->number = i;
return ptr;
}
}
void Library::displayNode(book *ptr) const
{
cout << ptr->number << ": " << ptr->tittle << endl;
}
void Library::displayList(book *ptr) const
{
if (!ptr)
cout << "Nothing to display" << endl;
while (ptr)
{
displayNode(ptr);
ptr = ptr->next;
}
}
main.cpp
#include "Library.h"
#include <iostream>
using namespace std;
int main()
{
Library a;
Library::book *ptrr;
ptrr = a.initNode("s1", 1);
a.addNode(ptrr);
ptrr = a.initNode("s2", 2);
a.addNode(ptrr);
a.displayList(a.head);
}

Answer 1

When you call the first a.addNode(ptrr) from main it does tail->next = newNode; (within Library::addNode), but, as tail is NULL (not assigned yet), it crashs....
Now, there could be other problems in the code, but this is most likely the first one that will make the program stop working...
Note that some stuff in your code could be simplified.
Like:
Library::book *Library::initNode(string s, int i)
{
book *ptr = new book;
if (ptr == NULL)
return static_cast<book *>(NULL);
else
{
ptr->tittle = s;
ptr->number = i;
return ptr;
}
}
could simply be:
Library::book *Library::initNode(string s, int i)
{
book *ptr = new book;
if (ptr != NULL)
{
ptr->tittle = s;
ptr->number = i;
}
return ptr;
}
And:
void Library::addNode(book *newNode)
{
if (head == NULL)
{
head = newNode;
head = newNode;
}
tail->next = newNode;
newNode->next = NULL;
tail = newNode;
}
Should be:
void Library::addNode(book *newNode)
{
if ( newNode != NULL ) // just in case
{
if (head == NULL)
{
head = newNode; // one is enough
}
if ( tail != NULL ) // to fix your crash
tail->next = newNode;
newNode->next = NULL;
tail = newNode;
}
}
Also, see user4581301 comment, the destructor code does not even compile....