# Inserting a Node

### Insert at Beginning :

```c
void insertAtBeginning(struct node *ptr, int data) {

    // Creating a new node
    struct node *newNode;
    newNode = (struct node *)malloc(sizeof(struct node));
    newNode -> data = data;
    
    // Make the new node as first node
    newNode -> next = head;
    head = newNode;

}
```

### Insert at N-th Position :

```c
void insertAtNthPos(struct node *ptr, int pos, int data) {

    // If position is invalid
    if (pos < 0 || pos > count(head)) {
        printf("Inavlid position\n");
        return;
    }
    
    else {
    
        // Creating a new node
        struct node *newNode;
        newNode = (struct node *)malloc(sizeof(struct node));
        newNode -> data = data;
    
        // For valid position, traverse to the position
        for (int i = 0; i < pos - 2; i++) {
            ptr = ptr -> next;
        }
        
        // Setting up links
        newNode -> next = ptr -> next;
        ptr -> next = newNode;
    }

}
```

{% hint style="info" %}
Indexing for the linked list is considered to start from 1 in the above code where the index of the first node is 1.

If index is considered to start from 0, change condition to **pos - 1** instead of **pos - 2** in the for loop.
{% endhint %}

### Insert at End in O(1) Time :

```c
void insertAtEnd(struct node *ptr, int data) {

    // Creating a new node
    struct node *newNode;
    newNode = (struct node *)malloc(sizeof(struct node));
    newNode -> data = data;
    newNode -> next = NULL;

    // If there are no nodes present
    if (head == NULL) {
        first = newNode;
        last = newNode;
    }
    
    // If some nodes are already present
    else {
        last -> next = newNode;
        last = newNode;
    }

}
```

{% hint style="info" %}
In the above function, an **additional pointer named last** is taken which will always point to the last node of the linked list. Through this, we can insert a new node to the end of list in constant time.
{% endhint %}

### Insert at End in O(n) Time :

```c
void insertAtEnd(struct node *ptr, int data) {

    // Creating a new node
    struct node *newNode;
    newNode = (struct node *)malloc(sizeof(struct node));
    newNode -> data = data;
    newNode -> next = NULL;

    // Traverse to last node
    while (ptr -> next != NULL) {
        ptr = ptr -> next;
    }
    ptr -> next = newNode;

}
```

Contributed by Nitin Ranganath