Question

#include<iostream>
using namespace std;

struct node {
    int data;
    node *link;
};
node *head = NULL;

void insert(int data, int n)
{
    node *temp = new node();
    temp->data = data;

    if (n == 1)
    {
        temp->link = head;
        head = temp;
    }

    else 
    {
        node* ptr = head;
        for (int i = 1; i <= n - 1; i++)
            ptr = ptr->link;
        temp->link = ptr->link;
        ptr->link = temp;
    }
}

void print()
{
    cout << "list is: ";
    node *temp = head;
    while (temp != NULL)
    {
        cout << temp->data << " ";
        temp = temp->link;
    }
    cout << endl;
}

int main()
{
    insert(2, 1);
    insert(3, 2);
    insert(4, 3);
    insert(5, 4);
    insert(6, 5);

    print();
    return 0;
}

This is a code to implement insertion in a linked list at nth position. The data and position are being passed from the main position.

I am not getting what is the possible error I have made, it has something to do with the for loop.

Its not executing, however if i make the following change:

for(int i=0;i<n-2;i++)

it works fine.

Answer 1

第一个insert(2,1)工作正常。所以你有这样的链接列表

(2)->NULL
 |
head

在第二个插入中，让我们跟随代码

1. else 
2. {
3.    node* ptr = head;
4.    for (int i = 1; i <= n - 1; i++)
5.        ptr = ptr->link;
6.    temp->link = ptr->link;
7.    ptr->link = temp;
8. }

第3行，ptr指向head。 n是2

(2)->NULL
 |
head
 |
ptr

第4行，1 <= (2-1)是true，因为1 == 1，所以for循环运行一次

第5行，ptr移动了一步，因此它指向NULL

(2)->NULL
 |    |
head  |
      |
     ptr

第6行，称为ptr->link，NULL->link。所以它在这里崩溃了。

当您执行for(int i=0;i<n-2;i++)时，n为2，因此0 < (2-2)为false，因此运行正常。注意：仅当按您的示例的顺序进行插入调用时，该功能才有效。如果以错误的顺序调用它们，它将无法正常工作。

将第6行更改为temp->link = ptr;，也应该在不更改循环的情况下起作用。

Answer 2

"Inserting a node in nth position in a linked list" :

Use a std::list rather than rolling your own. Then use std::list::insert.

Also; consider just using a std:: vector instead. A list is a terrible (pointer chasing, cache miss inducing) data structure to use on modern CPUs. A std::vector will almost always beat it (regardless of what your textbooks say about theoretical performance).

Inserting a node in nth position in a linked list

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