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Singly linked list Insertion and Deletion in C
We will look at all possible ways of insertion and deleting a node in a Single Linked List.


Things Discussed in the Post
We will be discussing the following in this post –
- Insertion in a Linked List
- At Start
- At end
- After a given position
- Deletion in a Linked List
- At start
- At end
- After a given position


First Lets understand what a Linked List is?
A linked List as the name suggests is a chain of linked data connected to one another in a sequential format just like a chain. A linked list has the following components in general –
- Data – This contains the data value held in any individual node of the linked list
- Next Pointer – This contains the address to the next node in a Linked List
Following are also some commonly used terminologies with a Linked List –
- Node – Individual component with its data and next pointer value together is called a node
- Head – The first node in the Linked List is called the head node.
- Tail – The last node in the Linked list is called as a tail node. Which points towards a NULL value.


Structure of Linked List
struct Node { int data; struct Node* next; };
Let us first Look at Insertion
Possible positions to insert –
- At Start
- At end
- A given position
Lets look at some pictures on how to insert and then we will look at the code –






Run
#include<stdio.h> #include<stdlib.h> struct Node{ int data; struct Node *next; }; void insertStart(struct Node** head, int data){ // dynamically create memory for this newNode struct Node* newNode = (struct Node*) malloc(sizeof(struct Node)); // assign data value newNode->data = data; // change the next node of this newNode // to current head of Linked List newNode->next = *head; //re-assign head to this newNode *head = newNode; } void insertEnd(struct Node** head, int data){ struct Node* newNode = (struct Node*) malloc(sizeof(struct Node)); newNode->data = data; // since this will be the last node so it will point to NULL newNode->next = NULL; // if the Linked List is empty this is the first node being entered if(*head==NULL){ *head = newNode; return; } // create another variable to traverse the LL // *head should not be used as we do not want to change head struct Node* temp = *head; // traverse to the last node of Linked List while(temp->next!=NULL) temp = temp->next; // assign last node's next to this newNode temp->next = newNode; } // required for insertAfter int getCurrSize(struct Node* node){ int size=0; while(node!=NULL){ node = node->next; size++; } return size; } void insertAfter(int n, int data, struct Node** head) { int size = getCurrSize(*head); // Can only insert after 1st position // Can't insert if position to insert is greater than size of Linked List if(n < 1 || n > size) printf("Invalid position to insert"); else { struct Node* newNode = (struct Node*) malloc(sizeof(struct Node)); newNode->data = data; newNode->next = NULL; // temp used to traverse the Linked List struct Node* temp = *head; // traverse till the nth node while(--n) temp=temp->next; // assign newNode's next to nth node's next newNode->next= temp->next; // assign nth node's next to this new node temp->next = newNode; // newNode inserted b/w 3rd and 4th node } } void display(struct Node* node){ // as linked list will end when Node is Null while(node!=NULL){ printf("%d ",node->data); node = node->next; } printf("\n"); } int main() { struct Node* head = NULL; // Need '&' i.e. address as we need to change head insertStart(&head,3); insertStart(&head,2); insertStart(&head,1); // no need for '&' as head need not be changed // only doing traversal display(head); insertEnd(&head,5); insertEnd(&head,6); insertEnd(&head,7); display(head); //Inserts data: 4 after 3rd position insertAfter(3,4,&head); display(head); return 0; }
Output
1 2 3 1 2 3 5 6 7 1 2 3 4 5 6 7
Let us Look at Deletion
Possible positions to delete –
- At Start
- At end
- A given position
Lets look at some pictures on how to delete and then we will look at the code –







Code for Delete from Start and Delete From End
#include<stdio.h>
#include<stdlib.h> struct Node{ int data; struct Node *next; }; void deleteStart(struct Node** head){ struct Node* temp = *head; // if there are no nodes in Linked List can't delete if(*head == NULL){ printf("Linked List Empty, nothing to delete"); return; } // move head to next node *head = (*head)->next; free(temp); } void deleteEnd(struct Node** head){ struct Node* temp = *head; struct Node* previous; // if there are no nodes in Linked List can't delete if(*head == NULL){ printf("Linked List Empty, nothing to delete"); return; } // if Linked List has only 1 node if(temp->next == NULL){ *head = NULL; return; } // else traverse to the last node while (temp->next != NULL) { // store previous link node as we need to change its next val previous = temp; temp = temp->next; } // Curr assign 2nd last node's next to Null previous->next = NULL; // delete the last node free(temp); // 2nd last now becomes the last node } void insertStart(struct Node** head, int data){ // dynamically create memory for this newNode struct Node* newNode = (struct Node*) malloc(sizeof(struct Node)); // assign data value newNode->data = data; // change the next node of this newNode // to current head of Linked List newNode->next = *head; //re-assign head to this newNode *head = newNode; } void display(struct Node* node){ // as linked list will end when Node is Null while(node!=NULL){ printf("%d ",node->data); node = node->next; } printf("\n"); } int main() { struct Node* head = NULL; // Need '&' i.e. address as we need to change head insertStart(&head,6); insertStart(&head,5); insertStart(&head,4); insertStart(&head,3); insertStart(&head,2); insertStart(&head,1); display(head); deleteStart(&head); display(head); deleteEnd(&head); display(head); return 0; }
Output
1 2 3 4 5 6 2 3 4 5 6 2 3 4 5



Deletion nth Node (A position)
Let us look at the code for deletion of a node at a position that is deletion nth node.
#include<stdio.h>
#include<stdlib.h> struct Node{ int data; struct Node *next; }; void deleteStart(struct Node** head); int getCurrSize(struct Node* node); // to delete nth node void deletePosition(struct Node** head, int n){ struct Node* temp = *head; struct Node* previous; //if the head node itself needs to be deleted int size = getCurrSize(*head); // not valid if(n < 1 || n > size){ printf("Enter valid position\n"); return; } // delete the first node if(n == 1){ deleteStart(head); return; } // traverse to the nth node while (--n) { // store previous link node as we need to change its next val previous = temp; temp = temp->next; } // change previous node's next node to nth node's next node previous->next = temp->next; // delete this nth node free(temp); } void deleteStart(struct Node** head){ struct Node* temp = *head; // if there are no nodes in Linked List can't delete if(*head == NULL){ printf("Linked List Empty, nothing to delete"); return; } // move head to next node *head = (*head)->next; free(temp); } // required for deletePosition int getCurrSize(struct Node* node){ int size=0; while(node!=NULL){ node = node->next; size++; } return size; } void insertStart(struct Node** head, int data){ // dynamically create memory for this newNode struct Node* newNode = (struct Node*) malloc(sizeof(struct Node)); // assign data value newNode->data = data; // change the next node of this newNode // to current head of Linked List newNode->next = *head; //re-assign head to this newNode *head = newNode; } void display(struct Node* node){ // as linked list will end when Node is Null while(node!=NULL){ printf("%d ",node->data); node = node->next; } printf("\n"); } int main() { struct Node* head = NULL; // Need '&' i.e. address as we need to change head insertStart(&head,5); insertStart(&head,4); insertStart(&head,3); insertStart(&head,2); insertStart(&head,1); display(head); // delete 3rd node deletePosition(&head, 3); display(head); // delete 1st node deletePosition(&head, 1); display(head); return 0; }
Output
1 2 3 4 5 1 2 4 5 2 4 5
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