Inserting a node at the beginning of linked list

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Linked List insertion can be done using three ways,

1) Insertion of a new node at the front of a given node.

2) Insertion of a new node after a given node.

3) Insertion of a new node at the end of the node.

In this tutorial, we will see how to insert a new node at the front of a given node. To understand this lets see the first scenario in which we have the linked list pointing a head pointer to the first node. The first node is pointing to the second one and at last, the third node is pointing to the NULL.

1) Before Insertion of node at the front

1) The original Linked list contains a head pointer pointing to first node.

2) First Node points to the second Node.

3) The second Node points to NULL.

Now, have a look at the second  scenario in which we are going to insert a node at the front side. For that thing to happen, we have to make the new node pointing towards the first node. Then the Head pointer should be pointing towards the new node and the first node pointing towards the second one. At last, the second node pointing towards the NULL.

2) After Insertion of node at front

Now if we want to insert a node at front of the linked list, it should be like,

1) New node pointing to the first Node.

2) Head pointer pointing to the new node .

3) First Node points to the second Node .

4) The second Node points to NULL.

So, this is how we can manipulate the nodes to insert and get the results in the linked list. Lets see a C function on how to insert a node at the front end of the linked list.

Function to insert a node at beginning of Linked List :

void insertAtFront (struct node ** headReference, int dataValue)
{
   /* 1. allocate node */
    struct node* new_node = (struct node*) malloc(sizeof(struct node));
  
  /* 2. put data into new node  */
    new_node->data  = dataValue;
  
  /* 3. Next of New Node is where the head is pointing right now. See in the figure. */
    new_node->next = (*headReference);
  
   /* 4. Point head to new node finally . */
    (*headReference)    = new_node;
}

Have a look at the given function. To insert a node at the front side of the linked list, we have created one new node. Then we have added some data or value inside that new node. In the third step, next of new node is pointing to head pointer's next node. Just keep diagram in mind and understand the terminology behind the insertion of nodes in Linked list. Then we updated the next pointer of head node to the new node in the fourth step.

I hope you got the concept and cheer us by sharing this article in your circle. In the next part of this linked list series, we will see how to insert a node after a given node. Tada..!!