CODEWITHSUNDEEP
c++linked-list
user2603796
user2603796

Reputation:

Simple Linked List insertion not working

I am writing a code for singly linked list and I am facing problem in writing its insert function. It is not inserting the new nodes and not printing them. I am not able to find the problem. Any help will be appreciated.

Code:

#include <iostream>

using namespace std;


class Node{
    int data;
    Node * next;

public:
    Node(int data_)
    {
        data = data_;
        next = nullptr;

    }

    void insert(int no)
    {
        Node * index = this->next;
        while (index != nullptr)
        {
            index = index->next;
        }
        index = new Node(no);
    }

    void print()
    {
        Node * index = this;
        while (index != nullptr)
        {
            cout << index->data << ", ";
            index = index->next;
        }
    }

};

int main()
{
    Node * head = new Node(1);
    head->insert(2);
    head->insert(3);
    head->insert(4);
    head->insert(5);

    head->print();

    system("pause");
    return 0;
}

Thanks

Upvotes: 0

Views: 102

Answers (2)

R Sahu
R Sahu

Reputation: 206717

It looks to me like you were trying to insert the new item at the tail of the list. You had a small error in your insert.

Here's a version that should work:

void insert(int no)
{
    Node* index = this;
    while (index->next != nullptr)
    {
        index = index->next;
    }
    index->next = new Node(no);
}

Explanation of error in your code

void insert(int no)
{
    Node * index = this->next;
    // When there is only one item in the linked list, which is true when
    // you are trying to insert the second item, index gets set to NULL.

    // The while loop does not get executed.
    while (index != nullptr)
    {
        index = index->next;
    }

    // index points to the newly created node but 'this' has no link
    // with index. As a consequence, 'this' never gets the second item appended
    // at the end.
    index = new Node(no);
}

Upvotes: 0

Edward
Edward

Reputation: 7100

Here's one way to fix your code:

class Node{
    int data;
    Node * next;

public:
    Node(int data_, Node *ptr=nullptr) : data(data_), next(ptr) {}  
    void insert(int no) { next = new Node(no, next); }
    void print() {
        cout << data;
        if (next != nullptr)
            next->print(); 
    }
};

Note the change in the constructor which makes things a little nicer and also note that there is no destructor at the moment so this will certainly leak memory until a proper destructor is defined.

The output of the program is now:

15432

Upvotes: 1

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