logical error in singly linked list code c++

Question

For the following code, the result that I'm aiming for is 4-->5-->, however the result that is outputted is only 4-->

For context, I'm trying to implement a singly linked list using structure and functions only in c++.

Code:

#include <iostream>
using namespace std;
struct node
{
    int data;
    node* next;
};
node* head = NULL;
void insert(int val)
{

    node* n = new node();
    n->data = val;


    if(head == NULL)
    {
        head = n;
    }
    else
    {
        node* temp = head;
        while(temp!=NULL)
        {
            temp = temp->next;
        }
        temp = n;
    }
}
void display()
{
    if(head == NULL)
    {
        cout<<"UNDERFLOW ! LINKED LIST IS EMPTY !"<<endl;
    }
    else
    {
        cout<<"LINKED LIST!"<<endl;
        node* temp = head;
        while(temp!=NULL)
        {
            cout<<temp->data<<"-->";
            temp = temp->next;
        }
        cout<<endl;
    }
}
int main()
{
    insert(4);
    insert(5);
    display();
    return 0;
}

Look real carefully at the append logic in insert. What's the value of temp when you assign n? — Stephen Newell
– Stephen Newell, Commented Dec 4, 2021 at 6:05

kiner_shah · Accepted Answer · 2021-12-04 06:37:40Z

1

As rightly pointed by @StephenNewell, you have a bug in the insert function.

Also in C++, use nullptr instead of NULL.

Change the below code in insert():

node* temp = head;
while(temp!=NULL)
{
    temp = temp->next;
}
temp = n;

to:

node* temp = head;
while (temp->next != nullptr)
{
    temp = temp->next;
}
temp->next = n;

answered Dec 4, 2021 at 6:37

kiner_shah

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2 Comments

jd singh Over a year ago

it was really helpful, thankyou😊.

kiner_shah Over a year ago

@jdsingh, if my answer was helpful, do consider up voting :-)

daohu527 · Accepted Answer · 2021-12-04 06:58:19Z

0

You question is temp is a temporary variable, and you just change the value of the temporary variable every time but not the last node of the linked list.

If you want to change the value of the pointer, you need the pointer of the pointer or You should change to

while(temp->next != NULL)
{
    temp = temp->next;
}
temp->next = n;

edited Dec 4, 2021 at 6:58

answered Dec 4, 2021 at 6:42

daohu527

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1 Comment

jd singh Over a year ago

thank you so much for helping me out😊.

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