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Linked list using pointers implementation: Runtime error (presumed due to pointers in a class)

popescustefanradu (2)
I'm trying to create a linked list using pointers.(full code at the bottom)

A node would look like this:
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template <class T>
struct elem
{
	T value;
	struct elem<T> *prev, *next;
};


While the list itself holds the first and last nodes using pointers.And introduces some functions in which I think i repeat the same mistake so i will only include 1 function.
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template <class T>
class LinkedList 
{
public: 
	struct elem<T> *first, *last;
	
	void addFirst(T x)
	{
		struct elem<T> *aux;
		aux=new struct elem<T>;
		aux->value=x;
		aux->prev=NULL;
		aux->next=first;
			
		if (first!=NULL) first->prev=aux; 
		first=aux;
		if (last==NULL) last=first;	
	}
}


When i test with something like this:
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int main()
{
	LinkedList<int> list1;
	list1.addFirst(89);
	list1.addFirst(34);
	list1.addLast(79);
	list1.addLast(34);
	list1.addFirst(89);
	list1.printList();
	
    list1.removeLastOccurrence(89);
	list1.printList();
	
    list1.removeLast();
	list1.removeFirst();
	list1.printList();
}


It goes into a runtime error probably inside the if (first!=NULL).
I don't know how to assign the first and last pointers as NULL by default.
If i do it inside the class where i declare the members it says ANSI C++ forbids initialisation of the respective members and also it makes them static.

Can anyone help me?

full code:
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#include <iostream.h>

template <class T>
struct elem
{
	T value;
	struct elem *prev, *next;
};

template <class T>
class LinkedList 
{
public: 
	struct elem<T> *first=NULL, *last=NULL;
	
	void addFirst(T x)
	{
		struct elem<T> *aux;
		aux=new struct elem<T>;
		aux->value=x;
		aux->prev=NULL;
		aux->next=first;
			
		if (first!=NULL) first->prev=aux; 
		first=aux;
		if (last==NULL) last=first;	
	}
	
	void addLast(T x)
	{
		struct elem<T> *aux;
		aux=new struct elem<T>;
		aux->value=x;
		aux->prev=last;
		aux->next=NULL;
		if (last!=NULL) last->next=aux;
		last=aux;
		if (first==NULL) first=last;
	}
	
	void removeFirst()
	{
		struct elem<T> *aux;
		if (first!=NULL)
		{
			aux=first;
			if (aux->next==NULL)
			{
				first=NULL;
				last=NULL;
				delete aux;
			}
			else
			{
				first=aux->next;
				first->prev=NULL;
				delete aux;
			}
		}
		else cout<<"Linked list is empty\r\n";
	}
	
	void removeLast()
	{
		struct elem<T> *aux;
		if (last!=NULL)
		{
			aux=last;
			if(aux->prev==NULL)
			{
				first=NULL;
				last=NULL;
				delete aux;
			}
			else 
			{
				last=aux->prev;
				last->next=NULL;
				delete aux;	
			}	
		}
		else cout<<"Linked list is empty\r\n";
	
	}
	
	struct elem<T>* findFirstOccurrence(T x)
	{
		struct elem<T>* aux;
		aux=first;
		while (aux!=NULL)
		{
			if (aux->value==x)	return aux;
			aux=aux->next;
		}
		return NULL;
	}
	
	struct elem<T>* findLastOccurence(T x)
	{
		struct elem<T>* aux;
		aux=last;
		while (aux!=NULL)
		{
			if(aux->value==x) return aux;
			aux=aux->prev;
		}
		return NULL;
	}
	
	void removeFirstOccurrence(T x)
	{
		struct elem<T>* aux;
		aux=first;
		while(aux!=NULL)
		{
			if(aux->value==x)
			{
				if (aux==first) {this.removeFirst(); break;}
				if (aux==last) {this.removeLast(); break;}
				aux->next->prev=aux->prev;
				aux->prev->next=aux->next;
				delete aux;
				break;
			}
		}
	
	}
	
	void removeLastOccurrence(T x)
	{
		struct elem<T>* aux;
		aux=last;
		while(aux!=NULL)
		{
			if(aux->value==x)
			{
				if (aux==first) {this->removeFirst(); break;}
				if (aux==last) {this->removeLast(); break;}
				aux->next->prev=aux->prev;
				aux->prev->next=aux->next;
				delete aux;
				break;
			}
		}
	}
	
	int isEmpty()
	{
		if (first==last==NULL) return 1;
		else return 0;	
	}
	
	void printList()
	{
		struct elem<T>* aux;
		aux=first;
		while (aux!=NULL)
		{
			cout<<aux->value<<" ";
			aux=aux->next;
		}
	}
};

int main()
{
	LinkedList<int> list1;
	list1.addFirst(89);
	list1.addFirst(34);
	list1.addLast(79);
	list1.addLast(34);
	list1.addFirst(89);
	list1.printList();
    list1.removeLastOccurrence(89);
	list1.printList();
    list1.removeLast();
	list1.removeFirst();
	list1.printList();
}


Last edited on
keskiverto (10363)
Write constructors for elem and LinkedList.
popescustefanradu (2)
I WUB YOU keskiverto. Ty! Lol, so much derp. This was my first C++ program so I still forget things that i should not.Ty very much.
Last edited on
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