C Exercises: Insert new node at the middle in a doubly linked list

C Doubly Linked List : Exercise-6 with Solution

Write a program in C to insert a new node in the middle of a doubly linked list.

Visual Presentation:

Sample Solution:

C Code:

#include <stdio.h>
#include <stdlib.h>

struct node {
    int num;
    struct node *preptr;
    struct node *nextptr;
} *stnode, *ennode;

// Function prototypes
void DlListcreation(int n);
void DlLinsertNodeAtMiddle(int num, int pos);
void displayDlList(int a);

int main() {
    int n, num1, a, insPlc;
    stnode = NULL;
    ennode = NULL;

    // User input for the number of nodes
    printf("\n\n Doubly Linked List : Insert new node at the middle in a doubly linked list :\n");
    printf("----------------------------------------------------------------------------------\n");
    printf(" Input the number of nodes (3 or more ): ");
    scanf("%d", &n);

    // Creating the doubly linked list
    DlListcreation(n);
    a = 1;
    displayDlList(a);

    // Inserting a node at a specified position
    printf(" Input the position ( 2 to %d ) to insert a new node : ", n - 1);
    scanf("%d", &insPlc);

    // Checking if the position is valid
    if (insPlc <= 1 || insPlc >= n) {
        printf("\n Invalid position. Try again.\n ");
    }
    if (insPlc > 1 && insPlc < n) {
        printf(" Input data for the position %d : ", insPlc);
        scanf("%d", &num1);
        DlLinsertNodeAtMiddle(num1, insPlc);
        a = 2;
        displayDlList(a);
    }
    return 0;
}

// Function to create a doubly linked list
void DlListcreation(int n) {
    int i, num;
    struct node *fnNode;

    if (n >= 1) {
        // Allocating memory for the first node
        stnode = (struct node *)malloc(sizeof(struct node));

        if (stnode != NULL) {
            // Input data for the first node
            printf(" Input data for node 1 : ");
            scanf("%d", &num);

            // Initializing values for the first node
            stnode->num = num;
            stnode->preptr = NULL;
            stnode->nextptr = NULL;
            ennode = stnode;

            // Loop to create subsequent nodes and link them
            for (i = 2; i <= n; i++) {
                fnNode = (struct node *)malloc(sizeof(struct node));
                if (fnNode != NULL) {
                    printf(" Input data for node %d : ", i);
                    scanf("%d", &num);
                    fnNode->num = num;
                    fnNode->preptr = ennode;    // Linking new node with the previous node
                    fnNode->nextptr = NULL;     // Setting next address of fnNode as NULL
                    ennode->nextptr = fnNode;   // Linking previous node with the new node
                    ennode = fnNode;            // Assigning new node as last node
                } else {
                    printf(" Memory can not be allocated.");
                    break;
                }
            }
        } else {
            printf(" Memory can not be allocated.");
        }
    }
}

// Function to insert a node at a specified position in the doubly linked list
void DlLinsertNodeAtMiddle(int num, int pos) {
    int i;
    struct node *newnode, *tmp;
    if (ennode == NULL) {
        printf(" No data found in the list!\n");
    } else {
        tmp = stnode;
        i = 1;
        while (i < pos - 1 && tmp != NULL) {
            tmp = tmp->nextptr;
            i++;
        }
        if (tmp != NULL) {
            newnode = (struct node *)malloc(sizeof(struct node));
            newnode->num = num;
            // Linking next address of new node with the next address of tmp node
            newnode->nextptr = tmp->nextptr;
            // Linking previous address of new node with the tmp node
            newnode->preptr = tmp;
            if (tmp->nextptr != NULL) {
                tmp->nextptr->preptr = newnode; // (n+1)th node is linking with new node
            }
            tmp->nextptr = newnode; // (n-1)th node is linking with new node 
        } else {
            printf(" The position you entered is invalid.\n");
        }
    }
}

// Function to display the doubly linked list
void displayDlList(int m) {
    struct node *tmp;
    int n = 1;
    if (stnode == NULL) {
        printf(" No data found in the List yet.");
    } else {
        tmp = stnode;
        if (m == 1) {
            printf("\n Data entered in the list are :\n");
        } else {
            printf("\n After insertion the new list are :\n");
        }
        // Loop to display nodes and their data
        while (tmp != NULL) {
            printf(" node %d : %d\n", n, tmp->num);
            n++;
            tmp = tmp->nextptr; // Moving the current pointer to the next node
        }
    }
}

Sample Output:

  Doubly Linked List : Insert new node at the middle in a doubly linked list :                                 
----------------------------------------------------------------------------------                            
 Input the number of nodes (3 or more ): 3                                                                    
 Input data for node 1 : 2                                                                                    
 Input data for node 2 : 4                                                                                    
 Input data for node 3 : 5                                                                                    
                                                                                                              
 Data entered in the list are :                                                                               
 node 1 : 2                                                                                                   
 node 2 : 4                                                                                                   
 node 3 : 5                                                                                                   
 Input the position ( 2 to 2 ) to insert a new node : 2                                                       
 Input data for the position 2 : 3                                                                            
                                                                                                              
 After insertion the new list are :                                                                           
 node 1 : 2                                                                                                   
 node 2 : 3                                                                                                   
 node 3 : 4                                                                                                   
 node 4 : 5

Flowchart:

DlListcreation() :

DlLinsertNodeAtMiddle() :

displayDlList() :

C Programming Code Editor:

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