Linking list

Linking_list.cpp

class listNode{
public:
  listNode *previous;
	listNode *next;
	int val;
	bool remove(){
		this->previous->next=this->next;
		this->next->previous=this->previous;
		delete this;
		return true;
	}
	bool isFirst(){
		return (this->previous->previous==NULL)?true:false;
	}
	bool isLast(){
		return (this->next->next==NULL)?true:false;
	}
};

class list{
	listNode* firstHeader;
	listNode* lastHeader;
public:
	list(){
		firstHeader = new listNode;
		lastHeader = new listNode;

		firstHeader->previous=NULL;
		firstHeader->next=lastHeader;
		lastHeader->previous=firstHeader;
		lastHeader->next=NULL;
	}
	listNode* addNode(int val){
		listNode* node = new listNode;
		node->val=val;

		node->previous=this->lastHeader->previous;
		node->next=this->lastHeader;

		this->lastHeader->previous->next=node;
		this->lastHeader->previous=node;

		return node;
	}
	bool isEmpty(){
		return (this->firstHeader->next->next==NULL)?true:false;
	}
	listNode* getFirst(){
		return (!this->isEmpty())?this->firstHeader->next:NULL;
	}
	listNode* getLast(){
		return (!this->isEmpty())?this->lastHeader->previous:NULL;
	}
	int getSize(){
		if(this->isEmpty())
			return 0;
		int i=0;
		listNode* n=this->getFirst();
		while(n){
			i++;
			if(n->isLast())
				break;
			n=n->next;
		}
		return i;
	}
	listNode* getByInd(int ind){
		int size=this->getSize();
		if(size==0||ind>=size)
			return NULL;
		listNode* n;
		int i;
		if(ind<size/2){
			i=0;
			n=this->getFirst();
			while(true){
				if(i==ind)
					break;
				n=n->next;
				i++;
			}
		}
		else{
			i=size-1;
			n=this->getLast();
			while(true){
				if(i==ind)
					break;
				n=n->previous;
				i--;
			}
		}
		return n;
	}
};

int main(){
	list* l1 = new list();
	l1->addNode(1);
	l1->addNode(2);
	l1->addNode(3)->remove();
	l1->addNode(4);
	l1->addNode(5);
	listNode* n=l1->getFirst();
	while(n){
		cout<<n->val<<endl;
		if(n->isLast())
			break;
		else
			n=n->next;
	}
	cout<<"Size = "<<l1->getSize()<<endl;
	cout<<"node = "<<l1->getByInd(2)->val<<endl;
	getch();
	return 0;
}