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How to destory the link list?

jimmy5023 (159)
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#include <iostream>

using namespace std;

const short unsigned int NUMVALS = 10;

struct ListNode {
	int value;
	ListNode* next;
};
ListNode* head = NULL;

bool insertNode(int num);
void displayList(void);
bool apendinglist (int num);

int main(void)
{
	int dumVals[NUMVALS];
	for (int i = 0; i<NUMVALS; i++)
	{
		cout<<"please enter your "<<i+1<<" number";
		cin>>dumVals[i];
	}
	short unsigned int i;
	for(i=0; i<NUMVALS; i++) { // insert the array values into the linked list
		if(insertNode(dumVals[i])) {
			cout << "Error in function insertNode!\n";
			cout << "Program will halt!\n";
			exit(1);
		}
	}

	displayList();
	
}

bool insertNode(int num)
// This function inserts a node into our linked list.
{
	ListNode* newNode;
	ListNode* nodePtr = head;
	ListNode* prevNodePtr = NULL;
	
	newNode = new ListNode;
	if(newNode == NULL) {
		cout << "Error allocating memory for new list member!\n";
		return 1;
	}

	newNode->value = num;
	newNode->next = NULL;

	if(head==NULL) { // check if list is currently empty
		cout << "List is currently empty - " << newNode->value;
		cout << " is part of the list's first node!\n";
		head = newNode;
	}
	else {
		while(nodePtr != NULL && nodePtr->value<num) {
			prevNodePtr = nodePtr;  // advance prevNodePtr up to nodePtr
			nodePtr = nodePtr->next;  // advance nodePtr by 1 node
		}
		if(prevNodePtr == NULL) {// at beginning of list
			newNode->next = head;
			head = newNode;
		}
		else {
			prevNodePtr->next = newNode;
			newNode->next = nodePtr;
		}
	}

	return 0;
}

void displayList(void)
// This function displays our linked list!
{
	ListNode* nodePtr = head;
	

	if(head == NULL) {
		cout << "List is currently empty!\n";
	}
	else {
		while (nodePtr != NULL) {
			cout << nodePtr->value << endl;
			nodePtr = nodePtr->next;
		}
	}
}

void deleteNode(int num)
// This function deletes a node, if it is in face there.
{
	ListNode* nodePtr = head;
	ListNode* prevNodePtr = NULL;
	
	if(head==NULL) { // list is currently empty
		cout << "The list is currently empty - ";
		cout << "There are no nodes to delete!\n";
	}
	else if(nodePtr->value == num) { // node is first one
		head = nodePtr->next;
		delete nodePtr;
	}
	else {
		while(nodePtr != NULL && nodePtr->value != num) {
			prevNodePtr = nodePtr;
			nodePtr = nodePtr->next;
		}
		if(nodePtr == NULL) {
			cout << "Your value (i.e., " << num << ")";
			cout << " was not in the list!\n";
		}
		else {
			prevNodePtr->next = nodePtr->next;
			delete nodePtr;
		}
	}
	
	return;
}

bool apendinglist(int num)
// This function inserts a node into our linked list.
{
	ListNode* newNode;
	ListNode* nodePtr = head;
	ListNode* prevNodePtr = NULL;
	
	newNode = new ListNode;
	if(newNode == NULL) {
		cout << "Error allocating memory for new list member!\n";
		return 1;
	}

	newNode->value = num;
	newNode->next = NULL;

	if(head==NULL) { // check if list is currently empty
		cout << "List is currently empty - " << newNode->value;
		cout << " is part of the list's first node!\n";
		head = newNode;
	}
	else 
	{
		while(nodePtr->next != NULL)
			nodePtr=nodePtr->next;
		nodePtr->next = newNode;
	}
	return 0;

	
}


I am to write a destructor that destory the link list.
~Listnode to destory the list, but i do not have the knowledge to destory the list. how i do that? My approach is to write a for loop on deleting node but i think that's not hte correct approach anyone would like to help?
Mathhead200 (1016)
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struct ListNode {
	ListNode* next;
	...

	//this will delete the whole list by just deleting the head
	// (if you don't want that, then you need to use a different approach like below)
	~ListNode() {
		if( next != NULL )
			delete next;
	}

	//another method
	static void recursiveDelete(ListNode *node) {
		if( node->next != NULL )
			recursiveDelete(node->next);
		delete node;
	}
};
Last edited on
jimmy5023 (159)
i add it but the "next" is having the red line under it why? i modify my code a little check it out. 
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#include <iostream>

using namespace std;

const short unsigned int NUMVALS = 10;

class linklist
{
private:
	struct ListNode
	{
		int value;
		ListNode* next;
	};
	ListNode *head;
public:
	linklist(void) {head = NULL;}
	static void recursiveDelete(linklist *node);
	
	bool insertNode(int num);
	void displayList(void);
	bool apendinglist (int num);
	bool deleteNode(int num);
};
int main(void)
{
	linklist mylist;
	int dumVals[NUMVALS];
	for (int i = 0; i<NUMVALS; i++)
	{
		cout<<"please enter your "<<i+1<<" number";
		cin>>dumVals[i];
	}
	short unsigned int i;
	for(i=0; i<NUMVALS; i++) { // insert the array values into the linked list
		if(mylist.insertNode(dumVals[i])) {
			cout << "Error in function insertNode!\n";
			cout << "Program will halt!\n";
			exit(1);
		}
	}

      mylist.displayList();
	
}

bool linklist::insertNode(int num)
// This function inserts a node into our linked list.
{
	ListNode* newNode;
	ListNode* nodePtr = head;
	ListNode* prevNodePtr = NULL;
	
	newNode = new ListNode;
	if(newNode == NULL) {
		cout << "Error allocating memory for new list member!\n";
		return 1;
	}

	newNode->value = num;
	newNode->next = NULL;

	if(head==NULL) { // check if list is currently empty
		cout << "List is currently empty - " << newNode->value;
		cout << " is part of the list's first node!\n";
		head = newNode;
	}
	else {
		while(nodePtr != NULL && nodePtr->value<num) {
			prevNodePtr = nodePtr;  // advance prevNodePtr up to nodePtr
			nodePtr = nodePtr->next;  // advance nodePtr by 1 node
		}
		if(prevNodePtr == NULL) {// at beginning of list
			newNode->next = head;
			head = newNode;
		}
		else {
			prevNodePtr->next = newNode;
			newNode->next = nodePtr;
		}
	}

	return 0;
}

void linklist::displayList(void)
// This function displays our linked list!
{
	ListNode* nodePtr = head;
	

	if(head == NULL) {
		cout << "List is currently empty!\n";
	}
	else {
		while (nodePtr != NULL) {
			cout << nodePtr->value << endl;
			nodePtr = nodePtr->next;
		}
	}
}

bool linklist::deleteNode(int num)
// This function deletes a node, if it is in face there.
{
	ListNode* nodePtr = head;
	ListNode* prevNodePtr = NULL;
	
	if(head==NULL) { // list is currently empty
		cout << "The list is currently empty - ";
		cout << "There are no nodes to delete!\n";
	}
	else if(nodePtr->value == num) { // node is first one
		head = nodePtr->next;
		delete nodePtr;
	}
	else {
		while(nodePtr != NULL && nodePtr->value != num) {
			prevNodePtr = nodePtr;
			nodePtr = nodePtr->next;
		}
		if(nodePtr == NULL) {
			cout << "Your value (i.e., " << num << ")";
			cout << " was not in the list!\n";
		}
		else {
			prevNodePtr->next = nodePtr->next;
			delete nodePtr;
		}
	}
	
	return 0;
}

bool linklist::apendinglist(int num)
// This function inserts a node into our linked list.
{
	ListNode* newNode;
	ListNode* nodePtr = head;
	ListNode* prevNodePtr = NULL;
	
	newNode = new ListNode;
	if(newNode == NULL) {
		cout << "Error allocating memory for new list member!\n";
		return 1;
	}

	newNode->value = num;
	newNode->next = NULL;

	if(head==NULL) { // check if list is currently empty
		cout << "List is currently empty - " << newNode->value;
		cout << " is part of the list's first node!\n";
		head = newNode;
	}
	else 
	{
		while(nodePtr->next != NULL)
			nodePtr=nodePtr->next;
		nodePtr->next = newNode;
	}
	return 0;

	
}

void linklist::recursiveDelete(linklist *node)
{
	if( node->next != NULL )
			recursiveDelete(node->next);
		delete node;
}
Mathhead200 (1016)
You want to delete the nodes ListNode *node

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class linklist
{
private:
	struct ListNode
	{
		...
		ListNode* next;

		//create the method here, as a member of ListNode
		static void recursiveDelete(ListNode *node);
	};
	ListNode *head;
public:
	linklist(void) {head = NULL;}
	~linklist() {
	  //invoke it when you delete the linklist
		if( head != NULL )
			recursiveDelete(head);
	}	
	...
};

//definition
void linklist::ListNode::recursiveDelete(linklist *node)
{
	if( node->next != NULL )
		recursiveDelete(node->next);
	delete node;
}
Last edited on
jimmy5023 (159)
it's still not letting me do this next,
there are 2 problems in your method
1)line 18, is not valid "recursiveDelete identifier not found"
2)line 24~29 voidlinklist::listnode::recursivedelete(linklist *) overloaded member function not found in linklist::listnode (ignore my cap mistakes). I fix it by changing linklist to ListNode, but i can't fix problem one.
Last edited on
Mathhead200 (1016)
Line 18: ListNode::recursiveDelete(head);
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