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

Last update on December 20 2024 13:18:40 (UTC/GMT +8 hours)

Write a program in C to insert a new node at the beginning of a Singly Linked List.

Visual Presentation:

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

Sample Solution:

C Code:

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

struct node 
{
    int num;                    //Data of the node
    struct node *nextptr;       //Address of the node
}*stnode;

void createNodeList(int n);     //function to create the list
void NodeInsertatBegin(int num);	            //function to insert node at the beginning
void displayList();             //function to display the list

int main()
{
    int n,num;
		printf("\n\n Linked List : Insert a new node at the beginning of a Singly Linked List:\n");
		printf("------------------------------------------------------------------------------\n");
    printf(" Input the number of nodes : ");
    scanf("%d", &n);
    createNodeList(n);
    printf("\n Data entered in the list are : \n");		
    displayList();
    printf("\n Input data to insert at the beginning of the list : ");
    scanf("%d", &num);
    NodeInsertatBegin(num);
    printf("\n Data after inserted in the list are : \n");		
    displayList();

    return 0;
}
void createNodeList(int n)
{
    struct node *fnNode, *tmp;
    int num, i;

    stnode = (struct node *)malloc(sizeof(struct node));
    if(stnode == NULL) //check whether the stnode is NULL and if so no memory allocation
    {
        printf(" Memory can not be allocated.");
    }
    else
    {
// reads data for the node through keyboard
        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 to linked list
        for(i=2; i<=n; i++)
        {
            fnNode = (struct node *)malloc(sizeof(struct node));


            if(fnNode == NULL) //check whether the fnnode is NULL and if so no memory allocation
            {
                printf(" Memory can not 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;
            }
        }
    }
} 

void NodeInsertatBegin(int num)
{
    struct node *fnNode;
    fnNode = (struct node*)malloc(sizeof(struct node));
    if(fnNode == NULL)
    {
        printf(" Memory can not be allocated.");
    }
    else
    {
        fnNode->num = num; //Links the data part
        fnNode->nextptr = stnode; //Links the address part
        stnode = fnNode; //Makes stnode as first node
    }
}

void displayList()
{
    struct node *tmp;
    if(stnode == NULL)
    {
        printf(" No data found in the 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 beginning of a Singly Linked List:                                    
------------------------------------------------------------------------------                                
 Input the number of nodes : 3                                                                                
 Input data for node 1 : 5                                                                                    
 Input data for node 2 : 6                                                                                    
 Input data for node 3 : 7                                                                                    
                                                                                                              
 Data entered in the list are :                                                                               
 Data = 5                                                                                                     
 Data = 6                                                                                                     
 Data = 7                                                                                                     
                                                                                                              
 Input data to insert at the beginning of the list : 4                                                        
                                                                                                              
 Data after inserted in the list are :                                                                        
 Data = 4                                                                                                     
 Data = 5                                                                                                     
 Data = 6                                                                                                     
 Data = 7

Flowchart: