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Linked List Data Structure | Insertion at the beginning

Introduction:
In this tutorial we are going to insert a new node at the beginning of the linked list.
There are two important point: first we should have a list and then we have to create a new node.

After creating the linked list and new node we will try to link our new node at the beginning of the list.


code for creating a list:

step1:
For creating the list first of all let's declare the structure of Nodes of the list:

struct Node{
int val;
struct Node *next;
};

step2: write main function:

int main(){

    int n;
    cout<<"enter the number of Nodes:";
    cin>>n;
    struct Node* head = NULL;
    struct Node* temp;
    int m;
    while(n--){
        cout<<"enter the data into nodes:";
        cin>>m;
        if(head==NULL){
            head = new Node();//creating a node
            head->val = m; // assigning value
            head->next=NULL;
            temp=head;//updating temp
        }
        else{
        struct Node *temp1 = new Node();//creating a node
        temp1->val = m;//assigning value
        temp1->next = NULL;
        temp->next = temp1; // linking temp with newly created node(temp1)
        temp=temp1;// shifting temp to newly created node(temp1)
        }
    }
 
}

now we have our list. second step is to create a new node. let's named it "newNode"

struct Node *newNode = new Node(); // after writing this line we have a new node.
newNode->val=7; //let's insert 7 in the value part of this node.
newNode->next = NULL;





Till now we have our linked list and we have our new node. now let's try to insert our newly created node at the beginning of the list.

what we have to do is, in the next field of our newly created node we have to put the address of the head of our linked list(cause head is the first node of the list).

newNode->next = head; // this piece of code will put the address of head node into the next field of newly created node. and this(newNode) will become the first node of the list. and we know that first node should be head. so we will make our newNode head of the list.



head=newNode; // this means now newnode will act as the head of the list.




full code:

#include<bits/stdc++.h>
using namespace std;

struct Node{
int val;
struct Node *next;
};

int main(){

    int n;
    cout<<"enter the number of Nodes:";
    cin>>n;
    struct Node* head = NULL;
    struct Node* temp;
    int m;
    while(n--){
        cout<<"enter the data into nodes:";
        cin>>m;
        if(head==NULL){
            head = new Node();//creating a node
            head->val = m; // assigning value
            head->next=NULL;
            temp=head;//updating temp
        }
        else{
        struct Node *temp1 = new Node();//creating a node
        temp1->val = m;//assigning value
        temp1->next = NULL;
        temp->next = temp1; // linking temp with newly created node(temp1)
        temp=temp1;// shifting temp to newly created node(temp1)
        }
    }

// till now we have created our list. after this we will create our new node .


struct Node *newNode = new Node(); // after writing this line we have a new node.
newNode->val=7; //let's insert 7 in the value part of this node.
newNode->next = NULL;

//now we have our new node also. so let's link it with the list.

newNode->next = head; // this piece of code will put the address of head node into the next field of newly created node.

head = newNode;// this means now newnode will act as the head of the list.

}

so in this post we have created our linked list, we create a new node and then this new node is inserted at the beginning of the list.

if you have any query please comment it down.

best of luck.

next tutorial:


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