Linked list

[cppnoob25]

I am working on writing a linked list and I'm just going off the concept of it for practice.

Does this look okay? I'm doing this for the purpose of learning and testing my knowledge.

#include <iostream>

using namespace std;

class List{
public:
    List();
    void push_back(int value);
    void push_front(int value);
    void pop_back();
    void pop_front();
    void print();


private:
    struct node{
        int data;
        node * next;
    };

    node * head;
    node * current;
    node *temp;

};

List::List()
{
    head = 0;
    current = 0;
    temp = 0;
}

void List::push_back(int value)
{
    node *n = new node;
    n->data = value;
    n->next = 0;

    if(head == 0)
    {
        head = n;
    }
    else{
        current = head;
        while(current->next != 0)
        {
            current = current->next;
        }
        current->next = n;
    }
}

void List::print()
{
    if(head == 0)
    {
        cout << "List is empty!" << endl;
    }
    else{
    current = head;
    while(current->next != 0)
    {
        cout << current->data << " ";
        current = current->next;
    }
    cout << current->data << " ";
    }
}

int main()
{
    List object;
    object.print();
    object.push_back(7);
    object.push_back(8);
    object.push_back(9);
    object.print();

}

[ResidentBiscuit]

The push_back does the job. You'll want to add insertion and deletion methods and some more constructors for basic linked list functionality.

Some issues:
You're not deleting nodes. You should write a destructor which does this (should also do it in your future insertion method).
You're not handling the situation where new fails.
You should use nullptr instead of 0 in modern C++.
Indention is not right on lines 61-67.
Keep your brace style consistent.
Don't include all of the std namespace at the global level.

Those should keep you going for a bit. Once you get a little more comfortable you should try to generalize the list to use any data type, not just int.

[cppnoob25]

Thanks for the feedback resident.

I do have one question though and how should I implement the destructor?

List::~List()
{

     //delete node; I know this won't compile.

}

After I finish this, I'll take a stab at using a template class to handle more data types.

[Little Captain]

The destructor's job should be to delete all the Nodes in the Linked List. For that, you'd have to iterate over the list, and save a pointer to the subsequent node before deleting the current one.
If you delete a node without saving its next pointer, you'll lose the rest of the list (and create a memory leak).

I created some videos for LinkedLists. Although they don't show how to delete a node (I might do that in the future), I still hope you'll find them useful.

https://www.youtube.com/watch?v=BrWXMfwmiQs&list=PLUTIHsaaB222qkK5_glKM1vzWS60O4VCi

[cppnoob25]

Thanks little. I looked at them.

So I tried this as my destructor.

List::~List()
{
    current = head;
    if(current->next == 0)
    {
        delete current;
    }
    else{
        while(current->next != 0)
        {
            temp = current->next;
            delete current;
            current = temp;
        }
        delete current;
    }

}

my only concern here is if I have to check if the list is empty initially? I'm assuming that if the current nodes next node is not pointing to 0 then the list is empty. I'm just not sure if my assumption here is correct.

[Little Captain]

Check if the head pointer points at a node or not. That's the way to determine if a list is empty or otherwise.

If you check the next pointer, then you're by default, assuming that there is a Node in the list with a next pointer to check.

So, to do that, do this:

if(current == nullptr) //Check if we are pointing at a head node or not.
{
    return; //If there is not even a head node, the list is empty and we return
}