I have given insert and a print function to insert data in a linked list and then print it.
But somehow it does not give any output and keeps running for a infinite time.
What is wrong?
Here is the code I have written. This is a simple program to create a linked list using loops and functions.
#include<iostream>
using namespace std;
struct node{
int data;
struct node* next;
};
struct node* head;
void insert(int data){
struct node* temphead=head;
if (temphead == NULL)
{
node* temp = new node();
temp->data=data;
temp->next=NULL;
while (temphead == NULL){
head==temp;
}
}
else if (temphead != NULL)
{
node* temp = new node();
temp->data=data;
temp->next=NULL;
while (temphead != NULL)
{
temphead->next= temp;
temphead=temphead->next;
}
}
}
void print(){
struct node* tempptr = head;
while (tempptr->next != NULL)
{
cout<<tempptr->data<<"_";
tempptr=tempptr->next;
}
}
int main(){
head=NULL;
insert(2);
insert(4);
insert(8);
insert(6);
//list - 2_4_8_6
print();
return 0;
}
There were few bugs in your code and also typos. Please read the comments marked with // CHANGE HERE for the description of the changes I did:
#include <iostream>
using namespace std;
struct node{
int data;
struct node* next;
};
struct node* head;
void insert(int data){
struct node* temphead = head;
if (temphead == nullptr)
{
node* temp = new node();
temp->data = data;
temp->next = nullptr;
// CHANGE HERE: removed unnecessary while loop
// Directly assign temp to head
head = temp;
}
else
{
node* temp = new node();
temp->data=data;
temp->next=nullptr;
// CHANGE HERE: check for temphead->next instead of temphead
while (temphead->next != nullptr)
{
// CHANGE HERE: remove unnecessary line: temphead->next= temp;
temphead=temphead->next;
}
// CHANGE HERE: assign temp to temphead->next (i.e. to last node)
temphead->next = temp;
}
}
void print(){
struct node* tempptr = head;
// CHANGE HERE: check for tempptr instead of tempptr->next
while (tempptr != nullptr)
{
cout<<tempptr->data<<"_";
tempptr=tempptr->next;
}
}
int main(){
head=nullptr;
insert(2);
insert(4);
insert(8);
insert(6);
//list - 2_4_8_6
print();
return 0;
}
NOTE: Your code uses new for dynamic memory allocation but doesn't use delete to de-allocate the memory when not required. If you want to avoid using new/delete, you can explore about smart pointers.
So I made these two simple functions regarding linked lists. One adds a node at the front and the other just displays the linked list in a sequence front to end. I'm wondering why this code wouldn't give me any output.
#include <iostream>
using namespace std;
class Node
{
public:
int data;
Node *next;
};
Node *head;
void addFront(Node *head, int item)
{
Node *temp = new Node();
temp->data = item;
temp->next = head;
head = temp;
}
void traverse(Node *head)
{
Node *temp = head;
while(temp!=NULL)
{
cout << temp->data << " ";
temp = temp->next;
}
}
int main()
{
addFront(head, 1);
addFront(head, 2);
addFront(head, 3);
traverse(head);
}
You're operating on a copy of head pointer in addFront(). You have
to pass a pointer to pointer:
void addFront(Node **head, int item)
The entire code could look like this:
#include <iostream>
using namespace std;
class Node
{
public:
int data;
Node *next;
};
Node *head;
void addFront(Node **head, int item)
{
Node *temp = new Node();
temp->data = item;
temp->next = *head;
*head = temp;
}
void traverse(Node *head)
{
Node *temp = head;
while(temp!=NULL)
{
cout << temp->data << " ";
temp = temp->next;
}
}
int main()
{
addFront(&head, 1);
addFront(&head, 2);
addFront(&head, 3);
traverse(head);
}
Argument of addFront is input as well as output. (Node *head)
It needs to be passed as referenced
I am trying to implement Linked List. In this sample program, user inputs an integer value (the number of strings to store in the list) and then strings one by one... But after several inputs (may be 4 or 5) the program crashes like the image here...
Even, I can't call any function more than 3 times at once which contains malloc() inside them..
I don't know why the problem is occurring. Help me fixing the issue....
#include <bits/stdc++.h>
using namespace std;
typedef struct Linked_List NODE;
struct Linked_List
{
string data;
NODE* next;
};
//Function prototypes
NODE *traverse(NODE *temp);
NODE* createNode(string data);
void preAppend(NODE* ln_list, string x);
NODE* find_data(NODE* ln_list, string data);
int main()
{
NODE* x=createNode("");
int t;
cin >>t;
string z;
while(t--)
{
cin >> z;
preAppend(x, z);
}
traverse(x);
return 0;
}
NODE *traverse(NODE *temp)
{
cout << temp->data << endl;
if(temp->next==NULL) return temp;
traverse(temp->next);
}
NODE* createNode(string data)
{
NODE* node = (NODE*)malloc(sizeof(NODE));
if(node==NULL)
{
printf("Error creating node (Error! Allocating Memory)\n");
exit(1);
}
node->data = data;
node->next = NULL;
}
void preAppend(NODE* ln_list, string x)
{
NODE* new_node = (NODE*)malloc(sizeof(NODE));
if(new_node==NULL)
{
printf("Error! Appending (Error Allocating Memory)\n");
exit(1);
}
new_node->data = x;
new_node->next = ln_list->next;
ln_list->next = new_node;
}
NODE* find_data(NODE* ln_list, string data)
{
NODE* current_node;
current_node = ln_list;
while(current_node->next!=NULL)
{
if(current_node->data == data)
{
return current_node;
}
current_node = current_node -> next ;
}
return NULL;
}
There are several problems in your code:
Usage of malloc instead of new
Using malloc for objects containing c++ objects (like stringin your case) won't call the constructors and therefore any operation upon the non constructed objects will fail.
If your program works without the return statements, it's because of undefined behaviour
Solution:
Replace
NODE* new_node = (NODE*)malloc(sizeof(NODE));
with
NODE* new_node = new NODE;
No return statements in non void functions
NODE *traverse(NODE *temp)
{
cout << temp->data << endl;
if (temp->next == NULL) return temp;
return traverse(temp->next); // return statement is needed here
}
NODE* createNode(string data)
{
NODE* node = new NODE;
if (node == NULL)
{
printf("Error creating node (Error! Allocating Memory)\n");
exit(1);
}
node->data = data;
node->next = NULL;
return node; // return statement needed here
}
Abuse of recursion
Using recursion in traverse may result in a stack overflow for long lists.
You should use a iterative approach. But you've found out that one already.
I uploaded the whole code at once. This method should work without any interruption
although if you want a complete understanding of each part i will recommend you to go over this article that i wrote on my website.
https://www.thebytewise.com/post/data-structure-and-algorithm-using-c-linear-linked-list-thebytewise
#include<stdio.h>
#include<stdlib.h>
void createList();
void traverseList();
struct node{
int data;
struct node *next;
}*header;
int main(){
int n;
printf("Enter the number of elements: ");
scanf("%d", &n);
createList(n);
printf("\nData in the list:\n");
traverseList(n);
return 0;
}
void createList(int n){
struct node *newNode, *temp;
int data, i;
newNode = (struct node *) malloc(sizeof(struct node));
if(newNode == NULL){
printf("ERROR: Memory Overflow");
}
else{
printf("Enter element 1: ");
scanf("%d", &data);
newNode->data = data;
newNode->next = NULL;
header = newNode;
temp = newNode;
for(i=2;i<=n;++i){
newNode = (struct node *) malloc(sizeof(struct node));
if(newNode == NULL){
printf("ERROR: Memory Overflow");
}
else{
printf("Enter element %d: ",i);
scanf("%d",&data);
newNode->data = data;
newNode->next = NULL;
temp->next = newNode;
temp = temp->next;
}
}
}
}
void traverseList(int n){
struct node *temp;
int i;
if(header == NULL){
printf("ERROR: Memory Underflow");
}
else{
temp = header;
for(i=0;i<n;++i){
printf("\ndata %d= %d",i+1, temp->data);
temp = temp->next;
}
}
}
I am a beginner and am working on Linked list. I am trying to make a program which adds elements to the list, updates the list, dislays it and deletes it.I am getting an exception : read access violation. temp was 0xDDDDDDDD.
I think there is some problem with display() function. The debugger also does shows the same.
#include "stdafx.h"
#include "Node.h"
#include<iostream>
using namespace std;
Node::Node() //constructor
{
head = NULL;
}
Node::~Node() //destructor
{
}
void Node::addFirstNode(int n) //adding the first element in the list
{
node *temp = new node;
temp->data = n;
temp->next = NULL;
head = temp;
}
void Node :: addLast(int n) //Adding elements at the end of the list
{
node *last = new node;
last->data = n;
last->next = NULL;
node *temp = new node;
temp = head;
while (temp->next != NULL) {
temp = temp->next;
}
temp->next = last;
}
void Node::display() //Displaying the list
{
node *temp = head;
while (temp != NULL)
{
cout<<temp->data;
temp = temp->next;
}
}
//the main function:
#include "stdafx.h"
#include "Node.h"
#include<iostream>
using namespace std;
int main()
{
Node a;
a.addFirstNode(101); //Calling function : addFirstNode
a.addLast(102); //Calling function : addLast
a.addLast(103); //Calling function : addLast
a.addLast(104); //Calling function : addLast
a.display(); //Calling function : display
return 0;
}
The Node.h file is as below:
struct node
{
int data;
node *next;
};
class Node
{
private :
node *head;
public:
Node();
~Node();
void addFirstNode(int n);
void addLast(int n);
void display();
};
You should rename Node to better describe what it is, e.g. List.
In Node::addFirst(), replace temp->next = NULL; with temp->next = head; You don't want to throw away your list every time you add a Node to the beginning of it.
In Node::addLast(), replace node *temp = new node; with node *temp = head; You don't want to leak memory every time you add a Node to the end of it.
I am about to create a linked that can insert and display until now:
struct Node {
int x;
Node *next;
};
This is my initialisation function which only will be called for the first Node:
void initNode(struct Node *head, int n){
head->x = n;
head->next = NULL;
}
To add the Node, and I think the reason why my linked list isn't working correct is in this function:
void addNode(struct Node *head, int n){
struct Node *NewNode = new Node;
NewNode-> x = n;
NewNode -> next = head;
head = NewNode;
}
My main function:
int _tmain(int argc, _TCHAR* argv[])
{
struct Node *head = new Node;
initNode(head, 5);
addNode(head, 10);
addNode(head, 20);
return 0;
}
Let me run the program as I think it works. First I initialise the head Node as a Node like this:
head = [ 5 | NULL ]
Then I add a new node with n = 10 and pass head as my argument.
NewNode = [ x | next ] where next points at head. And then I change the place where head is pointing to NewNode, since NewNode is the first Node in LinkedList now.
Why isn't this working? I would appreciate any hints that could make me move in the right direction. I think LinkedList is a bit hard to understand.
When I'm printing this, it only returns 5:
This is the most simple example I can think of in this case and is not tested. Please consider that this uses some bad practices and does not go the way you normally would go with C++ (initialize lists, separation of declaration and definition, and so on). But that are topics I can't cover here.
#include <iostream>
using namespace std;
class LinkedList{
// Struct inside the class LinkedList
// This is one node which is not needed by the caller. It is just
// for internal work.
struct Node {
int x;
Node *next;
};
// public member
public:
// constructor
LinkedList(){
head = NULL; // set head to NULL
}
// destructor
~LinkedList(){
Node *next = head;
while(next) { // iterate over all elements
Node *deleteMe = next;
next = next->next; // save pointer to the next element
delete deleteMe; // delete the current entry
}
}
// This prepends a new value at the beginning of the list
void addValue(int val){
Node *n = new Node(); // create new Node
n->x = val; // set value
n->next = head; // make the node point to the next node.
// If the list is empty, this is NULL, so the end of the list --> OK
head = n; // last but not least, make the head point at the new node.
}
// returns the first element in the list and deletes the Node.
// caution, no error-checking here!
int popValue(){
Node *n = head;
int ret = n->x;
head = head->next;
delete n;
return ret;
}
// private member
private:
Node *head; // this is the private member variable. It is just a pointer to the first Node
};
int main() {
LinkedList list;
list.addValue(5);
list.addValue(10);
list.addValue(20);
cout << list.popValue() << endl;
cout << list.popValue() << endl;
cout << list.popValue() << endl;
// because there is no error checking in popValue(), the following
// is undefined behavior. Probably the program will crash, because
// there are no more values in the list.
// cout << list.popValue() << endl;
return 0;
}
I would strongly suggest you to read a little bit about C++ and Object oriented programming. A good starting point could be this: http://www.galileocomputing.de/1278?GPP=opoo
EDIT: added a pop function and some output. As you can see the program pushes 3 values 5, 10, 20 and afterwards pops them. The order is reversed afterwards because this list works in stack mode (LIFO, Last in First out)
You should take reference of a head pointer. Otherwise the pointer modification is not visible outside of the function.
void addNode(struct Node *&head, int n){
struct Node *NewNode = new Node;
NewNode-> x = n;
NewNode -> next = head;
head = NewNode;
}
I'll join the fray. It's been too long since I've written C. Besides, there's no complete examples here anyway. The OP's code is basically C, so I went ahead and made it work with GCC.
The problems were covered before; the next pointer wasn't being advanced. That was the crux of the issue.
I also took the opportunity to make a suggested edit; instead of having two funcitons to malloc, I put it in initNode() and then used initNode() to malloc both (malloc is "the C new" if you will). I changed initNode() to return a pointer.
#include <stdlib.h>
#include <stdio.h>
// required to be declared before self-referential definition
struct Node;
struct Node {
int x;
struct Node *next;
};
struct Node* initNode( int n){
struct Node *head = malloc(sizeof(struct Node));
head->x = n;
head->next = NULL;
return head;
}
void addNode(struct Node **head, int n){
struct Node *NewNode = initNode( n );
NewNode -> next = *head;
*head = NewNode;
}
int main(int argc, char* argv[])
{
struct Node* head = initNode(5);
addNode(&head,10);
addNode(&head,20);
struct Node* cur = head;
do {
printf("Node # %p : %i\n",(void*)cur, cur->x );
} while ( ( cur = cur->next ) != NULL );
}
compilation: gcc -o ll ll.c
output:
Node # 0x9e0050 : 20
Node # 0x9e0030 : 10
Node # 0x9e0010 : 5
Below is a sample linkedlist
#include <string>
#include <iostream>
using namespace std;
template<class T>
class Node
{
public:
Node();
Node(const T& item, Node<T>* ptrnext = NULL);
T value;
Node<T> * next;
};
template<class T>
Node<T>::Node()
{
value = NULL;
next = NULL;
}
template<class T>
Node<T>::Node(const T& item, Node<T>* ptrnext = NULL)
{
this->value = item;
this->next = ptrnext;
}
template<class T>
class LinkedListClass
{
private:
Node<T> * Front;
Node<T> * Rear;
int Count;
public:
LinkedListClass();
~LinkedListClass();
void InsertFront(const T Item);
void InsertRear(const T Item);
void PrintList();
};
template<class T>
LinkedListClass<T>::LinkedListClass()
{
Front = NULL;
Rear = NULL;
}
template<class T>
void LinkedListClass<T>::InsertFront(const T Item)
{
if (Front == NULL)
{
Front = new Node<T>();
Front->value = Item;
Front->next = NULL;
Rear = new Node<T>();
Rear = Front;
}
else
{
Node<T> * newNode = new Node<T>();
newNode->value = Item;
newNode->next = Front;
Front = newNode;
}
}
template<class T>
void LinkedListClass<T>::InsertRear(const T Item)
{
if (Rear == NULL)
{
Rear = new Node<T>();
Rear->value = Item;
Rear->next = NULL;
Front = new Node<T>();
Front = Rear;
}
else
{
Node<T> * newNode = new Node<T>();
newNode->value = Item;
Rear->next = newNode;
Rear = newNode;
}
}
template<class T>
void LinkedListClass<T>::PrintList()
{
Node<T> * temp = Front;
while (temp->next != NULL)
{
cout << " " << temp->value << "";
if (temp != NULL)
{
temp = (temp->next);
}
else
{
break;
}
}
}
int main()
{
LinkedListClass<int> * LList = new LinkedListClass<int>();
LList->InsertFront(40);
LList->InsertFront(30);
LList->InsertFront(20);
LList->InsertFront(10);
LList->InsertRear(50);
LList->InsertRear(60);
LList->InsertRear(70);
LList->PrintList();
}
Both functions are wrong. First of all function initNode has a confusing name. It should be named as for example initList and should not do the task of addNode. That is, it should not add a value to the list.
In fact, there is not any sense in function initNode, because the initialization of the list can be done when the head is defined:
Node *head = nullptr;
or
Node *head = NULL;
So you can exclude function initNode from your design of the list.
Also in your code there is no need to specify the elaborated type name for the structure Node that is to specify keyword struct before name Node.
Function addNode shall change the original value of head. In your function realization you change only the copy of head passed as argument to the function.
The function could look as:
void addNode(Node **head, int n)
{
Node *NewNode = new Node {n, *head};
*head = NewNode;
}
Or if your compiler does not support the new syntax of initialization then you could write
void addNode(Node **head, int n)
{
Node *NewNode = new Node;
NewNode->x = n;
NewNode->next = *head;
*head = NewNode;
}
Or instead of using a pointer to pointer you could use a reference to pointer to Node. For example,
void addNode(Node * &head, int n)
{
Node *NewNode = new Node {n, head};
head = NewNode;
}
Or you could return an updated head from the function:
Node * addNode(Node *head, int n)
{
Node *NewNode = new Node {n, head};
head = NewNode;
return head;
}
And in main write:
head = addNode(head, 5);
The addNode function needs to be able to change head. As it's written now simply changes the local variable head (a parameter).
Changing the code to
void addNode(struct Node *& head, int n){
...
}
would solve this problem because now the head parameter is passed by reference and the called function can mutate it.
head is defined inside the main as follows.
struct Node *head = new Node;
But you are changing the head in addNode() and initNode() functions only. The changes are not reflected back on the main.
Make the declaration of the head as global and do not pass it to functions.
The functions should be as follows.
void initNode(int n){
head->x = n;
head->next = NULL;
}
void addNode(int n){
struct Node *NewNode = new Node;
NewNode-> x = n;
NewNode->next = head;
head = NewNode;
}
I think that, to make sure the indeep linkage of each node in the list, the addNode method must be like this:
void addNode(struct node *head, int n) {
if (head->Next == NULL) {
struct node *NewNode = new node;
NewNode->value = n;
NewNode->Next = NULL;
head->Next = NewNode;
}
else
addNode(head->Next, n);
}
Use:
#include<iostream>
using namespace std;
struct Node
{
int num;
Node *next;
};
Node *head = NULL;
Node *tail = NULL;
void AddnodeAtbeggining(){
Node *temp = new Node;
cout << "Enter the item";
cin >> temp->num;
temp->next = NULL;
if (head == NULL)
{
head = temp;
tail = temp;
}
else
{
temp->next = head;
head = temp;
}
}
void addnodeAtend()
{
Node *temp = new Node;
cout << "Enter the item";
cin >> temp->num;
temp->next = NULL;
if (head == NULL){
head = temp;
tail = temp;
}
else{
tail->next = temp;
tail = temp;
}
}
void displayNode()
{
cout << "\nDisplay Function\n";
Node *temp = head;
for(Node *temp = head; temp != NULL; temp = temp->next)
cout << temp->num << ",";
}
void deleteNode ()
{
for (Node *temp = head; temp != NULL; temp = temp->next)
delete head;
}
int main ()
{
AddnodeAtbeggining();
addnodeAtend();
displayNode();
deleteNode();
displayNode();
}
In a code there is a mistake:
void deleteNode ()
{
for (Node * temp = head; temp! = NULL; temp = temp-> next)
delete head;
}
It is necessary so:
for (; head != NULL; )
{
Node *temp = head;
head = temp->next;
delete temp;
}
Here is my implementation.
#include <iostream>
using namespace std;
template< class T>
struct node{
T m_data;
node* m_next_node;
node(T t_data, node* t_node) :
m_data(t_data), m_next_node(t_node){}
~node(){
std::cout << "Address :" << this << " Destroyed" << std::endl;
}
};
template<class T>
class linked_list {
public:
node<T>* m_list;
linked_list(): m_list(nullptr){}
void add_node(T t_data) {
node<T>* _new_node = new node<T>(t_data, nullptr);
_new_node->m_next_node = m_list;
m_list = _new_node;
}
void populate_nodes(node<T>* t_node) {
if (t_node != nullptr) {
std::cout << "Data =" << t_node->m_data
<< ", Address =" << t_node->m_next_node
<< std::endl;
populate_nodes(t_node->m_next_node);
}
}
void delete_nodes(node<T>* t_node) {
if (t_node != nullptr) {
delete_nodes(t_node->m_next_node);
}
delete(t_node);
}
};
int main()
{
linked_list<float>* _ll = new linked_list<float>();
_ll->add_node(1.3);
_ll->add_node(5.5);
_ll->add_node(10.1);
_ll->add_node(123);
_ll->add_node(4.5);
_ll->add_node(23.6);
_ll->add_node(2);
_ll->populate_nodes(_ll->m_list);
_ll->delete_nodes(_ll->m_list);
delete(_ll);
return 0;
}
link list by using node class and linked list class
this is just an example not the complete functionality of linklist, append function and printing a linklist is explained in the code
code :
#include<iostream>
using namespace std;
Node class
class Node{
public:
int data;
Node* next=NULL;
Node(int data)
{
this->data=data;
}
};
link list class named as ll
class ll{
public:
Node* head;
ll(Node* node)
{
this->head=node;
}
void append(int data)
{
Node* temp=this->head;
while(temp->next!=NULL)
{
temp=temp->next;
}
Node* newnode= new Node(data);
// newnode->data=data;
temp->next=newnode;
}
void print_list()
{ cout<<endl<<"printing entire link list"<<endl;
Node* temp= this->head;
while(temp->next!=NULL)
{
cout<<temp->data<<endl;
temp=temp->next;
}
cout<<temp->data<<endl;;
}
};
main function
int main()
{
cout<<"hello this is an example of link list in cpp using classes"<<endl;
ll list1(new Node(1));
list1.append(2);
list1.append(3);
list1.print_list();
}
thanks ❤❤❤
screenshot https://i.stack.imgur.com/C2D9y.jpg