can anyone help me with my linked list error please?-CodePudding

There is an issue with my code. I need to write a program that creates a linked list and performs insertion, deleting from the beginning, deleting from the end, and printing. Everything in the program works fine, but the delete the first node function. It throws an error in the printing function (posted a picture of the error below). Does anyone know what seems to be the problem? The function that deletes the last node works and prints perfectly.

LINKED LIST PROGRAM:

struct Node {
    int data;
    Node* next;
};

void insert(Node** head,int n) //insertion method
{
    Node* newNode = new Node;
    newNode->data = n;
    newNode->next = (*head);
    (*head) = newNode;
}

Node* deleteFront(struct Node* head)//deleting first node in the list
{
    if (head == NULL)
        return NULL;
    else
    {
        Node* t = head;
        head = head->next;
        free(t);
        t = NULL;
    }

    return head; 
}

Node* deleteEnd(struct Node* head)//deleting last node in the list
{
    if (head == NULL)
        return NULL;
    else if (head->next == NULL) {
        free(head);
        head = NULL;
    }
    else {
        Node* prev = head;
        Node* prev2 = head;

        while (prev->next != NULL)
        {
            prev2 = prev;
            prev = prev->next;
        }

        prev2->next = NULL;
        free(prev);
        prev = NULL;
    }

    return head;
}

void printLL(Node* h)
{
    while (h != NULL)
    {
        cout << h->data << " ";
        h = h->next;
    }

    cout << endl;
}

int main()
{
    cout << "Linked list question 2: " << endl;
    //linked list question 2
    Node* n = NULL;
    insert(&n, 60);
    insert(&n, 40);
    insert(&n, 20);
    printLL(n);

    deleteFront(n);
    cout << "after deleting first node: ";
    printLL(n);

    deleteEnd(n);
    cout << "after deleting last element: ";
    printLL(n);
}

A picture of the error:

CodePudding user response：

Since you're returning head in deleteFront(n) and deleteLast(n), however you're not updating head in main(). That's why its n is pointing to some garbage memory. Update your main() by storing head in n variable.

int main()
{
    cout << "Linked list question 2: " << endl;
    //linked list question 2
    Node* n = NULL;
    insert(&n, 60);
    insert(&n, 40);
    insert(&n, 20);
    printLL(n);

    n = deleteFront(n);
    cout << "after deleting first node: ";
    printLL(n);

    n = deleteEnd(n);
    cout << "after deleting last element: ";
    printLL(n);

}