Help with Linked List.

[cyrxe]

Hi. So here's the deal, I'm making a linked list program and everything went smoothly, until I added a if else statement in my remove method to try to catch whether a user entered value is in the list and deletes it, or outputs "Value not found" if not found.

The problem is that when I enter a string not found in the list, the program just terminates. I would appreciate if anyone could help.

Here's the program:

#include <iostream>
#include <string>

using namespace std;

void instructions();
string userInput();

class Node
{
    public:
        string data;
        Node *next;

        Node(string d)
        {
            data = d;
            next = NULL;
        }
        Node(string d, Node *n)
        {
            data = d;
            next = n;
        }


};

class linked
{
    Node *head;


    public:
        int counter;
        linked()
        {
            head = NULL;
            counter = 0;
        }

        bool isEmpty()
        {
            return head == NULL;
        }

        int size()
        {
            return counter;
        }

        void insert()
        {
            string d = userInput();
            Node *temp;
            if(head == NULL)
            {
                head = new Node(d, NULL);
                counter++;
                cout<<"Inserted: "<<head->data<<endl;
            }

            else
            {
                 temp = head;
                 while(temp->next !=NULL)
                    temp = temp->next;
                 temp->next = new Node(d, NULL);
                 counter++;
                 cout<<"Inserted: "<<temp->next->data<<endl;
            }

        }

        string delhead()
        {
            Node *temp = head;
            head = head->next;
            return temp->data;
        }

        void remove()
        {
            int x;
            string d = userInput();
            if(head == NULL)
                cout<<"The list is Empty."<<endl;
            else if(head->data.compare(d) == 0)
                cout<<"Removed: "<<delhead()<<endl;
            else
            {
                Node *temp = head;
                for(x=0; x<=counter; x++)
                {
                    if(temp->next->data.compare(d) == 0)
                        break;
                    else
                        temp = temp->next;
                }

                if(x>=0)
                {
                    Node *rem = temp->next;
                    temp->next = temp->next->next;
                    counter--;
                    cout<<"Removed: "<<rem->data<<endl;
                }
                else
                    cout<<"Value entered not found."<<endl;
            }


        }

        void display()
        {
            Node *temp;
            temp = head;
            while(temp != NULL)
            {
                cout<<temp->data<<endl;
                temp = temp->next;
            }

        }

};

int main(void)
{
    linked ln;
    int choice;

    do
    {
        instructions();
        cout<<"? ";
        cin>>choice;
        cin.ignore();

        switch(choice)
        {
            case 1:
                ln.insert();
                break;

            case 2:
                ln.remove();
                break;
            case 3:
                ln.display();
                break;
            case 4:
                cout<<"Goodbye!"<<endl;
                break;
            default:
                cout<<"Invalid Choice! Try Again..."<<endl;
                break;
        }

    }while(choice != 4);

    cin.get();
    return 0;
}

void instructions()
{
    cout<<"1. Insert\n2. Delete\n3. Display\n4. Exit"<<endl;
}

string userInput()
{
    string value;
    cout<<"Enter Value: ";
    getline (cin, value);

    return value;
}

Here's the problematic output:

1. Insert
2. Delete
3. Display
4. Exit
? 1
Enter Value: asd
Inserted: asd
1. Insert
2. Delete
3. Display
4. Exit
? 2
Enter value: d

Process returned -1 (0xFFFFFFFF) execution time: 9.982 s
Press Enter to Continue

I've been at this for the past hour and to no avail, I can't figure out what's wrong.

[ne555]

Suppose that you've got 1 element in your list. counter = 0

               Node *temp = head;
                for(x=0; x<=counter; x++) //¿how many times is the loop executed?
                {
                    if(temp->next->data.compare(d) == 0) //¿which element are you looking at?
                        break;
                    else
                        temp = temp->next;
                }

[cyrxe]

@ne555 Ah, so you mean when it accesses the the temp->next-data when there is really no temp->next->data then it exit abnormally??

[cyrxe]

Got it sorted out. Thanks for the help ne555. I did not think that it would terminate incorrectly if it accesses something not there. Thanks again!