04 - Doubly Linked List -(Own Implementation)

Using tail to reduce the loops for reaching last node for insertion and deletion.
With NULL available at end of Last node, while(temp != NULL) can be used to iterate over the full length of the list in length().
The length counter need not be incremented after the loop ends since it is Going till NULL which is next of tail so count will be right.
This iterates over all values of list without leaving the last node also, so it useful for Display() and Search() functions.
Or for(let i=0; i<length() ; i++) for similar result.
Check Circular Doubly Linked List for More Info on changes and reasons.

Final Implementation

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

struct node
{
	int data;
	struct node *prev;
	struct node *next;
} *head = NULL, *tail = NULL, *new = NULL;

void Inserter(int ch, int ele);
void Deleter(int ch);
void Display();
void Search();
int length();

int main()
{
	int ch, ele;
	while(1)
	{
		printf("\n1. Insert at Beginning\t2. Insert inBetween\t3. Insert at End\n");
		printf("4. Delete Beginning\t5. Delete inBetween\t6. Delete End\n");
		printf("7. Display\t8. Search\t0. Exit\n");
		printf("Enter a Choice: ");
		
		scanf("%d", &ch);
		printf("\n");
		
		switch(ch)
		{
			case 0:
				exit(0);
			case 1:
			case 2:
			case 3:
				printf("\nEnter the value to Insert: ");
				scanf("%d", &ele);
				Inserter(ch, ele);
				Display();
				break;
			case 4:
			case 5:
			case 6:
				Deleter(ch);
				Display();
				break;
			case 7:
				Display();
				printf("\nLength is: %d\n", length());
				break;
			case 8:
				Search();
				break;
		}
	}
	return 0;
}
void firstNode(int ele)
{
	new = (struct node*) malloc(sizeof(struct node));
	new->data = ele;
	
	new->next = new->prev = NULL;
	head = tail = new;
}
void inB(int ele)
{
	new = (struct node*) malloc(sizeof(struct node));
	new->data = ele;

	new->next = head;
	new->prev = NULL;

	head->prev = new;
	head = new;
}
void inE(int ele)
{
	new = (struct node*) malloc(sizeof(struct node));
	new->data = ele;

	new->prev = tail;
	new->next = NULL;
	
	tail->next = new;
	tail = new;
}
int length()
{
	if(head == NULL)
		return 0; // No Element

	if(head == tail)
		return 1; // One Element

	struct node *temp = head;
	int len = 0;
	while(temp != NULL) // (temp != tail) can also be used
	{
		len++;
		temp = temp->next;
	}
	// No need of len++, All elements traversed 
	return len; 
}
int getPos()
{
	int len = length();
	
	int pos;
	printf("\nEnter Position: ");
	scanf("%d", &pos);
	
	// Regect Invalid positions -1, 0, len+2
	if(pos <= 0 || pos > len+1)
	{
		printf("\nInvalid Location \n");
		return -1;
	}
	return pos;
}
void inM(int ele)
{
	int pos = getPos();
	int len = length();
	
	if(pos == -1) // handling Invalid Positons
		return;
		
	if(pos == 1) // Handling 1st Position
	{
		inB(ele);
		return;
	}
	if(pos == len+1) // Last position len+1
	{
		inE(ele);
		return;
	}
	
	// Inserting at Middle Positions
	struct node *temp = head;
	
	for(int i=2; i<pos; i++)
	{
		temp = temp->next;		
	}
	
	new = (struct node*) malloc(sizeof(struct node));
	new->data = ele;

	new->next = temp->next;
	new->prev = temp;
	
	temp->next->prev = new;
	temp->next = new;
}
void Inserter(int ch, int ele)
{
	if(head == NULL)
	{
		firstNode(ele);
		return;
	}
	switch(ch)
	{
		case 1:
			inB(ele);
			break;
		case 2:
			inM(ele);
			break;
		case 3:
			inE(ele);
			break;
	}
}
void Display()
{
	if(head == NULL)
	{
		printf("\nNo Elements to display\n");
		return;
	}
	// Traverse till end using length
	int len = length();
	
	struct node *temp = head;
	for(int i = 0; i<length(); i++)
	{
		printf("%d <-> ", temp->data);
		temp = temp->next;
	}
	printf("Null\n");
	
	printf("\nTotal elements are : %d\n\n", length());
}
void delB()
{
	struct node *temp = head;
	
	head = head->next;
	head->prev = NULL;
	free(temp);
}
void delE()
{
	struct node *temp = tail;
	
	tail = tail->prev;
	tail->next = NULL;
	free(temp);
}
void delM()
{
	int pos = getPos();
	int len = length();

	// Handle invalid possitions, -1, 0, len+2
	// Also handle len+1, no node to delete there 
	if(pos == -1 || pos == len+1)
		return;

	if(pos == 1) // Delete First
	{
		delB();
		return;
	}
	if(pos == len) // Delete Last
	{
		delE();
		return;
	}

	struct node *temp = head;

	for( int i=1 ; i<pos ; i++)
	{
		temp = temp->next;
	}
	// Used i=1 so temp is on the node to be deleted
	// Works in Doubly linked list only because prev can be accessed
	// in Singly linked i=2 works better to stop before node
	
	temp->prev->next = temp->next;
	temp->next->prev = temp->prev;
	free(temp);
}
void Deleter(int ch)
{
	if(head == NULL)  // No Elements
	{
		printf("\nNothing to delete\n");
		return;
	}
	if( head == tail) // One Element
	{
		struct node *temp = head;
		head = tail = NULL;  // Reset
		free(temp);	
		return;
	}

	// There are more than 1 elements
	switch(ch)
	{
		case 4:
			delB();
			break;
		case 5:
			delM();
			break;
		case 6:
			delE();
			break;
	}
}


void Search()
{
	if(head == NULL)
	{
		printf("\nNo values\n");
		return;
	}
	
	int ele;
	printf("\nEnter the Value to search: ");
	scanf("%d", &ele);
	
	int found = 0;	
	struct node *temp = head;
	
	for(int i=0 ; i<length() ; i++ )
	{
		if (temp->data == ele)
		{
			printf("\nElement %d found at index %d\n", ele, i);
			found =1;
			break;
		}
		// Moving temp to next node
		temp = temp->next;		
	}
	// if found still 0, No Match Found
	if(!found)
		printf("\nElement %d was not found.\n", ele);
}

// Since NULL is available while() can be used similar to length()

//	int pos = 0;
//	while(temp != NULL)
//	{
//		if(temp->data == ele)
//		{
//			printf("\nValue %d found at %d location\n", ele, pos);
//			return;
//		}
//		pos++;
//		temp = temp->next;
//	}
//	printf("\nElement %d not found in list\n", ele);

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

struct node
{
	int data;
	struct node *prev;
	struct node *next;
} *head = NULL, *tail = NULL, *new = NULL;

void Inserter(int ch, int ele);
void Deleter(int ch);
void Display();
void Search();
int length();

int main()
{
	int ch, ele;
	while(1)
	{
		printf("\n1. Insert at Beginning\t2. Insert inBetween\t3. Insert at End\n");
		printf("4. Delete Beginning\t5. Delete inBetween\t6. Delete End\n");
		printf("7. Display\t8. Search\t0. Exit\n");
		printf("Enter a Choice: ");
		
		scanf("%d", &ch);
		printf("\n");
		
		switch(ch)
		{
			case 0:
				exit(0);
			case 1:
			case 2:
			case 3:
				printf("\nEnter the value to Insert: ");
				scanf("%d", &ele);
				Inserter(ch, ele);
				Display();
				break;
			case 4:
			case 5:
			case 6:
				Deleter(ch);
				Display();
				break;
			case 7:
				Display();
				printf("\nLength is: %d\n", length());
				break;
			case 8:
				Search();
				break;
		}
	}
	return 0;
}
void firstNode(int ele)
{
	new = (struct node*) malloc(sizeof(struct node));
	new->data = ele;
	
	new->next = NULL;
	new->prev = NULL;
	head = new;
	tail = new;
}
void inB(int ele)
{
	new = (struct node*) malloc(sizeof(struct node));
	new->data = ele;

	new->next = head;
	head->prev = new;
	head = new;
}
void inE(int ele)
{
	new = (struct node*) malloc(sizeof(struct node));
	new->data = ele;

	new->prev = tail;
	tail->next = new;

	new->next = NULL;
	tail = new;
}
int length()
{
	if(head == NULL)
	{
		return 0;
	}
	struct node *temp = head;
	int len = 0;

	while(temp != NULL)
	{
		len++;
		temp = temp->next;
	}
	return len;
}
int getPos()
{
	int pos;
	printf("\nEnter Position: ");
	scanf("%d", &pos);

	if(pos <= 0 || pos > length()+1)
	{
		printf("\nInvalid Location \n");
		return -1;
	}
	return pos;
}
void inM(int ele)
{
	int pos = getPos();

	if(pos == -1)
		return;
	if(pos == 1)
	{
		inB(ele);
		return;
	}
	if(pos == length()+1)
	{
		inE(ele);
		return;
	}

	int i = 2;
	struct node *temp = head;
	
	while( i < pos)
	{
		temp = temp->next;
		i++;
	}
	
	new = (struct node*) malloc(sizeof(struct node));
	new->data = ele;

	new->next = temp->next;
	temp->next->prev = new;
	new->prev = temp;
	temp->next = new;
}
void Inserter(int ch, int ele)
{
	if(head == NULL)
	{
		firstNode(ele);
		return;
	}
	switch(ch)
	{
		case 1:
			inB(ele);
			break;
		case 2:
			inM(ele);
			break;
		case 3:
			inE(ele);
			break;
	}
}
void delB()
{
	struct node *temp = head;
	head = head->next;
	head->prev = NULL;
	free(temp);
}
void delE()
{
	struct node *temp = tail;
	tail = tail->prev;
	tail->next = NULL;
	free(temp);
}
void delM()
{
	int pos = getPos();

	if(pos == -1 || pos == length()+1)
		return;

	if(pos == 1)
	{
		delB();
		return;
	}
	if(pos == length())
	{
		delE();
		return;
	}

	struct node *temp = head;
	 
	int i = 1;
	while( i < pos)
	{
		temp = temp->next;
		i++;
	}
	temp->prev->next = temp->next;
	temp->next->prev = temp->prev;
	free(temp);
}
void Deleter(int ch)
{
	if(head == NULL)
	{
		printf("\nNo elements in List\n");
		return;
	}
	if( head == tail)
	{
		struct node *temp = head;
		head = tail = NULL;
		free(temp);	
		return;
	}
	switch(ch)
	{
		case 4:
			delB();
			break;
		case 5:
			delM();
			break;
		case 6:
			delE();
			break;
	}
}
void Display()
{
	if(head == NULL)
	{
		printf("\nNo Elements to display\n");
		return;
	}
	struct node *temp = head;
	while(temp != NULL)
	{
		printf("%d -> ", temp->data );
		temp = temp->next;
	}
	printf("\nTotal elements are : %d\n\n", length());
}

void Search()
{
	if(head == NULL)
	{
		printf("\nNo values\n");
		return;
	}
	int ele;
	printf("\nEnter the Value to search: ");
	scanf("%d", &ele);

	int pos = 0;
	struct node *temp = head;
	while(temp != NULL)
	{
		if(temp->data == ele)
		{
			printf("\nValue %d found at %d location\n", ele, pos);
			return;
		}
		pos++;
		temp = temp->next;
	}
	printf("\nElement %d not found in list\n", ele);
}

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

struct node 
{
    int data;
    struct node *prev;
    struct node *next;
} *head = NULL, *new = NULL;

int len; // Global length variable

// Function to calculate the length of the linked list
int length() 
{
    struct node *temp = head;
    int count = 0;
    
    while (temp != NULL) {
        count++;
        temp = temp->next;
    }
    return count;
}

// Insert at the beginning
void Begin(int a) 
{
    new = (struct node*)malloc(sizeof(struct node));
    new->data = a;
    new->prev = NULL;
    new->next = NULL;

    if (head == NULL) { 
        head = new;
    } else {
        new->next = head;  
        head->prev = new;  
        head = new;         // Update head to new node
    }
}

// Insert at the end
void End(int a) 
{
    struct node *temp = head;
    new = (struct node*)malloc(sizeof(struct node));
    new->data = a;
    new->next = NULL;

    if (head == NULL) {
        new->prev = NULL;
        head = new;
        return;
    }

    while (temp->next != NULL) {
        temp = temp->next;
    }

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

// Insert in the middle
void Middle(int a) 
{
    struct node *temp;
    int loc, i = 1;
    len = length();

    if (len == 0) {
        printf("The list is Empty\n");
        return;
    }

    printf("Enter the location to be inserted: ");
    scanf("%d", &loc);

    if (loc > len || loc < 1) {
        printf("Invalid Location\n");
        return;
    }

    temp = head;
    while (i < loc) {
        temp = temp->next;
        i++;
    }

    new = (struct node*)malloc(sizeof(struct node));
    new->data = a;

    new->next = temp->next;
    new->prev = temp;
    
    if (temp->next != NULL) 
    {
        temp->next->prev = new;
    }

    temp->next = new;
}

// Search for an element
void Search(int key) {
    struct node *temp = head;
    int pos = 1, found = 0;

    if (head == NULL) {
        printf("The list is empty. Cannot search.\n");
        return;
    }

    while (temp != NULL) {
        if (temp->data == key) {
            printf("Element %d found at position %d\n", key, pos);
            found = 1;
            break;
        }
        temp = temp->next;
        pos++;
    }

    if (!found) {
        printf("Element %d not found in the list.\n", key);
    }
}

// Delete from the beginning
void DBegin() {
    struct node *temp;
    if (head == NULL) {
        printf("The list is empty\n");
        return;
    }

    temp = head;
    head = head->next;

    if (head != NULL) {
        head->prev = NULL;
    }

    free(temp);
}

// Delete from the middle
void DMid() {
    struct node *temp;
    int loc, i = 1;
    len = length();

    if (len == 0) {
        printf("The list is empty\n");
        return;
    }

    printf("Enter the position to delete: ");
    scanf("%d", &loc);

    if (loc > len || loc < 1) {
        printf("Invalid Location\n");
        return;
    }

    temp = head;
    while (i < loc) {
        temp = temp->next;
        i++;
    }

    if (temp->prev != NULL) {
        temp->prev->next = temp->next;
    } else { 
        head = temp->next; // If deleting the first node, update head
    }

    if (temp->next != NULL) {
        temp->next->prev = temp->prev;
    }

    free(temp);
}

// Delete from the end
void DEnd() {
    struct node *temp = head;

    if (head == NULL) {
        printf("The list is empty, nothing to delete.\n");
        return;
    }

    if (head->next == NULL) { // Only one node in the list
        free(head);
        head = NULL;
        printf("Last node deleted, list is now empty.\n");
        return;
    }

    while (temp->next != NULL) {
        temp = temp->next;
    }

    temp->prev->next = NULL; // Second last node becomes last
    free(temp);
    printf("Last node deleted successfully.\n");
}

// Display the linked list
void Display() 
{
    struct node *temp;
    if (head == NULL) {
        printf("The list is empty\n");
        return;
    }

    temp = head;
    while (temp != NULL) {
        printf("%d <-> ", temp->data);
        temp = temp->next;
    }
    printf("NULL\n");

    len = length();
    printf("Total Elements: %d\n", len);
}

int main() {
    int a, ch;

    while (1) {
        printf("\n1. Insert Beginning\n");
        printf("2. Insert Middle\n");
        printf("3. Insert End\n");
        printf("4. Display\n");
        printf("5. Search\n");
        printf("6. Delete Beginning\n");
        printf("7. Delete Middle\n");
        printf("8. Delete End\n");
        printf("9. Exit\n");
        printf("Enter choice: ");
        scanf("%d", &ch);

        switch (ch) {
            case 1:
                printf("Enter the element to be inserted: ");
                scanf("%d", &a);
                Begin(a);
                break;
            case 2:
                printf("Enter the element to be inserted: ");
                scanf("%d", &a);
                Middle(a);
                break;
            case 3:
                printf("Enter the element to be inserted: ");
                scanf("%d", &a);
                End(a);
                break;
            case 4:
                Display();
                break;
            case 5:
                printf("Enter the element to search: ");
                scanf("%d", &a);
                Search(a);
                break;
            case 6:
                DBegin();
                break;
            case 7:
                DMid();
                break;
            case 8:
                DEnd();
                break;
            case 9:
                printf("Exiting...\n");
                return 0;
            default:
                printf("Enter a valid choice!\n");
        }
    }
}

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03 - Circular Singly Linked List -(Own Implementation)

05 - Circular Doubly Linked List -(Own Implementation)

Sujith's Library

Title here

04 - Doubly Linked List -(Own Implementation)

Final Implementation