what is the problem in the display function ?  the code :    #include using namespace std; class node { public:     int data;     node* next; }; void display(node * head) // printing the data of the nodes {     node* temp = head;     while (temp != NULL) {         cout << temp->data << endl;         temp = temp->next;     } } // add                                                 void push(node** head, int newdata)                    // { 5, 10 , 20 , 30 , 40 } {     node* newnode = new node();     newnode->data = newdata;     newnode->next = *head;     *head = newnode; } void append(node** head, int newdata)                // { 10 , 20 , 30 , 40 } {     node* newnode = new node();     newnode->data = newdata;     newnode->next = NULL;     node* last = *head;     if (*head == NULL) {         *head = newnode;         return;     }     while (last->next != NULL)     {         last = last->next;     }     last->next = newnode; } void insertafter(node* previousnode, int newdata)    // { 10 , 15 , 20 , 30 , 40 } {     if (previousnode == NULL) {         cout << "The previous node cannot be NULL";     }     node* newnode = new node();     newnode->data = newdata;     newnode->next = previousnode->next;     previousnode->next = newnode; } //delete void remove(node* head, int target) // { 10 , 20 , 30 , 40 } {     node* node2del;     node* temp;     temp = head;     if (temp != NULL) {         if (temp->data == target) {             free(temp);             head = head->next;             //delete(temp);             return;         }         while (temp->next != NULL) {             if (temp->next->data == target) {                 node2del = temp->next;                 temp->next = temp->next->next;                 free(node2del);                 return;             }             temp = temp->next;         }         if (temp->data != target) {             cout << "the item is not in the list %d" << target;         }     }     return; } int main() {     node* head = new node();     node* second = new node();     node* third = new node();     node* fourth = new node();     head->data = 10;     head->next = second;     second->data = 20;     second->next = third;     third->data = 30;     third->next = fourth;     fourth->data = 40;     fourth->next = NULL;     cout << "\nDisplay the linked list items \n";     display(head);     /*cout << "\nPUSH \n";     push(&head, 5);     display(head);*/     /*cout << "\nappend \n";     append(&head, 100);     display(head);*/     //cout << "\nInsert after \n";  // { 10 , 20 , 30 , 15 , 40 }     //insertafter(head->next->next, 15);     //display(head);     remove(head, 10);     cout << "\nafter Delete \n";     display(head); }

what is the problem in the display function ? 

the code : 

#include <iostream>
using namespace std;

class node
{
public:
    int data;
    node* next;
};

void display(node * head) // printing the data of the nodes
{
    node* temp = head;

    while (temp != NULL) {
        cout << temp->data << endl;
        temp = temp->next;
    }
}

// add                                                
void push(node** head, int newdata)                    // { 5, 10 , 20 , 30 , 40 }
{
    node* newnode = new node();
    newnode->data = newdata;
    newnode->next = *head;
    *head = newnode;
}

void append(node** head, int newdata)                // { 10 , 20 , 30 , 40 }
{
    node* newnode = new node();
    newnode->data = newdata;
    newnode->next = NULL;

    node* last = *head;

    if (*head == NULL) {
        *head = newnode;
        return;
    }

    while (last->next != NULL)
    {
        last = last->next;
    }
    last->next = newnode;
}

void insertafter(node* previousnode, int newdata)    // { 10 , 15 , 20 , 30 , 40 }
{
    if (previousnode == NULL) {
        cout << "The previous node cannot be NULL";
    }
    node* newnode = new node();
    newnode->data = newdata;
    newnode->next = previousnode->next;
    previousnode->next = newnode;

}

//delete
void remove(node* head, int target) // { 10 , 20 , 30 , 40 }
{
    node* node2del;
    node* temp;
    temp = head;
    if (temp != NULL) {
        if (temp->data == target) {
            free(temp);
            head = head->next;
            //delete(temp);
            return;
        }
        while (temp->next != NULL) {
            if (temp->next->data == target) {
                node2del = temp->next;
                temp->next = temp->next->next;
                free(node2del);
                return;
            }
            temp = temp->next;
        }
        if (temp->data != target) {
            cout << "the item is not in the list %d" << target;

        }
    }
    return;
}

int main()
{
    node* head = new node();
    node* second = new node();
    node* third = new node();
    node* fourth = new node();

    head->data = 10;
    head->next = second;

    second->data = 20;
    second->next = third;

    third->data = 30;
    third->next = fourth;

    fourth->data = 40;
    fourth->next = NULL;

    cout << "\nDisplay the linked list items \n";
    display(head);

    /*cout << "\nPUSH \n";
    push(&head, 5);
    display(head);*/

    /*cout << "\nappend \n";
    append(&head, 100);
    display(head);*/

    //cout << "\nInsert after \n";  // { 10 , 20 , 30 , 15 , 40 }
    //insertafter(head->next->next, 15);
    //display(head);

    remove(head, 10);
    cout << "\nafter Delete \n";
    display(head);
}