C Program to Insert a Node Before a given Node in Singly Linked List | codeitwise

Here we are going to write a c program to insert node before a given node in singly linked list. Before we proceed, if you don't have basic knowledge of linked list or want to learn everything about singly linked list at one go then you must visit singly linked list post which is a part of our dsa series and also types of linked list series.

Ok Now How will we do this means insertion of node before a given node in singly linked list.

We first allocate memory space for new node. Then we will take a pointer variable temp and initialize it with HEAD that is, temp will point to the first node. Then we will store the value to be inserted in new node's data part. In while loop, we will traverse through the linked list to reach the node before which we want to insert new node. Once reached, we will point the next pointer in such a way that the new node is inserted before desired node.

Algorithm-

Step 1: If AVAIL = NULL

        Write overflow

        Go to Step 10

    [End of If]

Step 2: Set NEW_NODE = AVAIL

Step 3: Set AVAIL = AVAIL ➡ NEXT

Step 4: Set NEW_NODE ➡ DATA = VAL

Step 5: Set PTR = HEAD

Step 6: Repeat Step 7 while PTR ➡ NEXT ➡ DATA!= VAL

Step 7: Set PTR = PTR ➡ NEXT

    [End of Loop]

Step 8: Set NEW_NODE ➡ NEXT = PTR ➡ NEXT

Step 9: Set PTR ➡ NEXT = NEW_NODE

Step 10: EXIT

C program to insert a node before a given node in singly linked list-

#include <stdio.h>
#include <malloc.h>

struct node
{
    int data;
    struct node* next;
};

void insertatend(struct node** head)
{
    int n;
    printf("Enter value to insert at end: ");
    scanf("%d",&n);
    struct node* val=(struct node*)malloc(sizeof(struct node));
    val->data=n;
    val->next=NULL;
    if(*head==NULL)
    {
        *head=val;
        return;
    }
    struct node* t=*head;
    while(t->next!=NULL)
    {
        t=t->next;
    }
    t->next=val;
}

void insertbeforenode(struct node** head)
{
    int n;
    printf("Enter value of node before which you want to insert : ");
    scanf("%d",&n);
    struct node* nw=(struct node*)malloc(sizeof(struct node));
    struct node* temp=*head;
    while(temp->next->data!=n)
    {
        temp=temp->next;
    }
    nw->data=12;
    nw->next=temp->next;
    temp->next=nw;
}

void display(struct node* head)
{
    struct node* t=head;
    while(t!=NULL)
    {
        printf("%d => ",t->data);
        t=t->next;
    }
    printf("NULL \n");
    
}

int main()
{
    struct node* head=NULL;
    insertatend(&head);
    insertatend(&head);
    insertatend(&head);
    display(head);
    insertbeforenode(&head);
    display(head);
    return 0;
}

Output-

Enter value to insert at end: 9
Enter value to insert at end: 10
Enter value to insert at end: 11
9 => 10 => 11 => NULL 
Enter value of node before which you want to insert : 10
9 => 12 => 10 => 11 => NULL 

Visual Representation-

Related Programs-

C Program to Insert a Node at the beginning of Singly linked list

C Program to Insert a Node at the end of Singly Linked List

C Program to Insert a Node after a given Node in Singly Linked List