DS Practical Slip 7 Q A

C Program to Create a Doubly Linked List and Display Nodes with Odd Values

A Doubly Linked List is a data structure where each node contains data, a pointer to the next node, and a pointer to the previous node. In this program, we will create a doubly linked list and display only the nodes containing odd values.

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📝 Problem Statement

Q1. A) Write a ‘C’ program to create a doubly linked list and display nodes having odd value.

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💡 Logic (Simple Student-Friendly Steps)

🔹 Create Operation

1. Define a structure for a node with:
   • data
   • prev pointer
   • next pointer
2. For each new node:
   • Allocate memory using malloc().
   • Assign the value to the node.
   • If list is empty, make it head.
   • Otherwise, attach the node at the end.

🔹 Display Odd Nodes

1. Start from head.
2. Traverse using the next pointer.
3. Check if data % 2 != 0.
4. If yes, print the value.

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💻 Source Code (Student-Friendly)

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

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

int main()
{
    struct node *head = NULL, *newnode, *temp;
    int n, i, value;

    printf("Enter number of nodes: ");
    scanf("%d", &n);

    for(i = 0; i < n; i++)
    {
        printf("Enter value for node %d: ", i+1);
        scanf("%d", &value);

        newnode = (struct node*)malloc(sizeof(struct node));
        newnode->data = value;
        newnode->prev = NULL;
        newnode->next = NULL;

        if(head == NULL)
        {
            head = newnode;
        }
        else
        {
            temp = head;
            while(temp->next != NULL)
                temp = temp->next;

            temp->next = newnode;
            newnode->prev = temp;
        }
    }

    printf("Nodes with odd values are:\n");
    temp = head;
    while(temp != NULL)
    {
        if(temp->data % 2 != 0)
            printf("%d ", temp->data);

        temp = temp->next;
    }

    return 0;
}

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🖥️ Sample Output

Enter number of nodes: 5
Enter value for node 1: 10
Enter value for node 2: 15
Enter value for node 3: 20
Enter value for node 4: 25
Enter value for node 5: 30
Nodes with odd values are:
15 25

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🎓 Viva Questions with Answers

1. What is a doubly linked list?

A linked list where each node has a next and a previous pointer.

2. How do you identify odd values?

By checking if data % 2 != 0.

3. What is the first node called?

The head node.

4. How is a new node added at the end?

By traversing to the last node and updating its next pointer to the new node.

5. What is the advantage of a doubly linked list over a singly linked list?

It allows traversal forward and backward.