trouble implementing a linked list

Question

I'm trying to implement a simple link list. The initial value is inserted successfully, but the next elements are not entered properly. Please help me resolve what the error is. Thanks in appreciation.

#include<iostream>

using std::cout;

class node
{
    public:
        node():next(0){}
        void setNext(node *next){ next = next; }
        node* getNext(){ return next; }
        void setValue(int val){ value = val; }
        int getValue(){ return value; }

    private:
        int value;
        node *next;
};

class list
{
    public:
        list():head(new node()),len(0){}
        bool insert(int value);
        //bool remove(int value);
        int valueAt(int index);
        int length();

    private:
        node *head;
        int len;

};

bool list::insert(int value)
{
    node *current = 0;
    node *previous = 0;
    node *temp = 0;

    temp = new node();
    temp->setValue(value);

    current = head;
    previous = head;

    while((temp->getValue())>(current->getValue()))
    {
        previous = current;
        current = current->getNext();

        if(!current)
        {
            break;
        }
    }

    if(current == head)
    {
        temp->setNext(current);
        head = temp;

        len++;
    }
    else
    {
        temp->setNext(current);
        previous->setNext(temp);

        len++;
    }
}

int list::valueAt(int index)
{
    if((index < len) && (index >= 0))
    {
        node *current = 0;
        current = head;
        int count = 0;

        while(count < index)
        {
            current = current->getNext();
            count++;
        }

        return (current->getValue());
    }
    else
    {
        return -1;
    }
}


int main()
{
    list myList;

    myList.insert(5);
    myList.insert(20);
    myList.insert(10);

    cout<<"Value at index 1 : "<<myList.valueAt(1);

    return 0;
}

Seth Carnegie · Accepted Answer · 2011-06-06 18:14:37Z

3

After a cursory glance, perhaps the problem is

void setNext(node *next){ next = next; }

You are assigning a variable to itself, because local variables overshadow instance variables. Try changing that to

void setNext(node *next){ this->next = next; }

In other notes:

In list::list, you probably shouldn't initialize head to a new node. This will mean your linked list will have one arbitrary node on creation but have a length of 0. You should think about setting head to NULL instead.
On creation, nodes have a random value. Consider requiring a parameter for that in the constructor, or an appropriate default value.
-1 is a bad "invalid value" for list::valueAt because it's also a valid value for a node to store.
You should probably rename the list class to slist to indicate it stores values in sorted order.

edited Jun 6, 2011 at 18:14

answered Jun 6, 2011 at 17:18

Seth Carnegie

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