C Exercises: Insert a new node at the middle of the Linked List

Last update on December 20 2024 13:06:21 (UTC/GMT +8 hours)

Write a program in C to insert a node in the middle of a Singly Linked List.

Visual Presentation:

C Exercises: Insert a new node at the middle of the Linked List

Sample Solution:

C Code:

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

// Structure to define a node in a linked list
struct node 
{
    int num;                    // Data of the node
    struct node *nextptr;       // Address of the next node
}*stnode;                       // Pointer to the starting node

// Function prototypes
void createNodeList(int n);             // Function to create the linked list
void insertNodeAtMiddle(int num, int pos); // Function to insert a node at a given position
void displayList();                     // Function to display the linked list

// Main function
int main()
{
    int n, num, pos;

    // Displaying the purpose of the program
    printf("\n\n Linked List : Insert a new node at the middle of the Linked List :\n");
    printf("-----------------------------------------------------------------------\n");
	
    // Inputting the number of nodes for the linked list
    printf(" Input the number of nodes (3 or more) : ");
    scanf("%d", &n);

    // Creating the linked list with n nodes
    createNodeList(n);
    printf("\n Data entered in the list are : \n");		
    displayList();

    // Inputting data and position to insert in the middle of the list
    printf("\n Input data to insert in the middle of the list : ");
    scanf("%d", &num);
    printf(" Input the position to insert new node : ");
    scanf("%d", &pos);

    // Checking if insertion is possible at the given position
    if(pos <= 1 || pos >= n)
    {
        printf("\n Insertion cannot be possible in that position.\n");
    }
    else if(pos > 1 && pos < n)
    {
        insertNodeAtMiddle(num, pos);
        printf("\n Insertion completed successfully.\n");
    }

    // Displaying the updated list
    printf("\n The new list is : \n");
    displayList();

    return 0;
}

// Function to create a linked list with n nodes
void createNodeList(int n)
{
    struct node *fnNode, *tmp;
    int num, i;
    stnode = (struct node *)malloc(sizeof(struct node));
    if(stnode == NULL) // Check whether stnode is NULL for memory allocation
    {
        printf(" Memory cannot be allocated.");
    }
    else
    {
        // Reading data for the first node
        printf(" Input data for node 1 : ");
        scanf("%d", &num);
        stnode->num = num;      
        stnode->nextptr = NULL; // Links the address field to NULL
        tmp = stnode;

        // Creates n nodes and adds them to the linked list
        for(i = 2; i <= n; i++)
        {
            fnNode = (struct node *)malloc(sizeof(struct node));
            if(fnNode == NULL) // Check whether fnNode is NULL for memory allocation
            {
                printf(" Memory cannot be allocated.");
                break;
            }
            else
            {
                printf(" Input data for node %d : ", i);
                scanf(" %d", &num);
                fnNode->num = num;      // Links the num field of fnNode with num
                fnNode->nextptr = NULL; // Links the address field of fnNode with NULL
                tmp->nextptr = fnNode; // Links previous node i.e. tmp to the fnNode
                tmp = tmp->nextptr;
            }
        }
    }
} 

// Function to insert a node at a specified position in the list
void insertNodeAtMiddle(int num, int pos)
{
    int i;
    struct node *fnNode, *tmp;
    fnNode = (struct node*)malloc(sizeof(struct node));
    if(fnNode == NULL) // Check whether fnNode is NULL for memory allocation
    {
        printf(" Memory cannot be allocated.");
    }
    else
    {
        fnNode->num = num; // Links the data part
        fnNode->nextptr = NULL;
        tmp = stnode;
        for(i = 2; i <= pos - 1; i++)
        {
            tmp = tmp->nextptr;
            if(tmp == NULL)
                break;
        }
        if(tmp != NULL)
        {
            fnNode->nextptr = tmp->nextptr;  // Links the address part of new node
            tmp->nextptr = fnNode;   
        }
        else
        {
            printf(" Insertion is not possible at the given position.\n");
        }
    }
}

// Function to display the linked list
void displayList()
{
    struct node *tmp;
    if(stnode == NULL)
    {
        printf(" No data found in the empty list.");
    }
    else
    {
        tmp = stnode;
        while(tmp != NULL)
        {
            printf(" Data = %d\n", tmp->num);   // Prints the data of current node
            tmp = tmp->nextptr;                 // Advances the position of current node
        }
    }
}

Sample Output:

Linked List : Insert a new node at the middle of the Linked List :                                           
-----------------------------------------------------------------------                                       
 Input the number of nodes (3 or more) : 4                                                                    
 Input data for node 1 : 1                                                                                    
 Input data for node 2 : 2                                                                                    
 Input data for node 3 : 3                                                                                    
 Input data for node 4 : 4                                                                                    
                                                                                                              
 Data entered in the list are :                                                                               
 Data = 1                                                                                                     
 Data = 2                                                                                                     
 Data = 3                                                                                                     
 Data = 4                                                                                                     
                                                                                                              
 Input data to insert in the middle of the list : 5                                                           
 Input the position to insert new node : 3                                                                    
                                                                                                              
 Insertion completed successfully. 
 The new list are :                                                                                           
 Data = 1                                                                                                     
 Data = 2                                                                                                     
 Data = 5                                                                                                     
 Data = 3                                                                                                     
 Data = 4

Flowchart: