Question

This much like the single linked list assignment. I am giving you the majority of the code and left a couple of functions for you to complete. I had intended to try to do some video clips of my own lecture but I am not going to have time to get those completed (at least not at a quality I want).   You might take a look at these sites for more help outside just zyBooks.
#include <stdio.h>
#include <stdlib.h>

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

struct node *createList(struct node *start);
void displayList(struct node *start);
struct node *insertInEmptyList(struct node *start, int data);
struct node *insertInBeginning(struct node *start, int data);
void insertAtEnd(struct node *start, int data);
void insertAfter(struct node *start, int data, int x);
struct node *insertBefore(struct node *start, int data, int x);
struct node *deleteNode(struct node *start, int data);
struct node *reverseList(struct node *start);

main()
{
        int choice, data, x;
        struct node *start=NULL;

        start=createList(start);

        while(1)
        {
                printf("\n");
                printf("1.Display List\n");
                printf("2.Insert in empty list\n");
                printf("3.Insert a node in beginning of the list\n");
                printf("4.Insert a node at the end of the list\n");
                printf("5.Insert a node after a specified node\n");
                printf("6.Insert a node before a specified node\n");
                printf("7.Delete a node\n");
                printf("8.Reverse the list\n");
                printf("9.Quit\n");
                printf("Enter your choice : ");
                scanf("%d", &choice);

        if (choice == 9)
                break;

        switch(choice)
        {
                case 1:
                        displayList(start);
                        break;
                case 2:
                        printf("Enter the element to be inserted : ");
                        scanf("%d", &data);
                        start=insertInEmptyList(start,data);
                        break;
                case 3:
                        printf("Enter the element to be inserted : ");
                        scanf("%d", &data);
                        start=insertInBeginning(start, data);
                        break;
                case 4:
                        printf("Enter the element to be inserted : ");
                        scanf("%d", &data);
                        insertAtEnd(start, data);
                        break;
                case 5:
                        printf("Enter the element to be insert : ");
                        scanf("%d", &data);
                        printf("Enter the element after which to insert : ");
                        scanf("%d", &x);
                        insertAfter(start, data, x);
                        break;
                case 6:
                        printf("Enter the element to be inserted : ");
                        scanf("%d", &data);
                        printf("Enter the element before which to insrt : ");
                        scanf("%d", &x);
                        start=insertBefore(start, data, x);
                        break;
                case 7:
                        printf("Enter the element to be deleted : ");
                        scanf("%d", &data);
                        start=deleteNode(start, data);
                        break;
                case 8:
                        start=reverseList(start);
                        break;
                default:
                        printf("Wrong choice\n");

                }       //end of switch
        } //end of while
} //end of main


struct node *createList(struct node *start)
{
        int i, n, data;
        printf("Enter the number of nodes : ");
        scanf("%d", &n);
        start=NULL;

        if (n==0)
                return start;

        printf("Enter the first element to be inserted : ");
        scanf("%d", &data);
        start=insertInEmptyList(start, data);

        for (i=2; i<=n; i++)
        {
                printf("Enter the next element to be inserted : ");
                scanf("%d", &data);
                insertAtEnd(start, data);
        }
        return start;
}//End of createList()


void displayList(struct node *start)
{
        struct node *p;
        if (start==NULL)
        {
                printf("List is empty\n");
                return;
        }

        p=start;
        printf("List is :\n");
        while(p!=NULL)
        {
                printf("%d ", p->info);
                p=p->next;
        }
        printf("\n");
} //End of displayList()

struct node *insertInEmptyList(struct node *start, int data)
{
        **********************************
        *** COMPLETE THE REQUIRED CODE ***
        **********************************
}//End of insertInEmptyList()

struct node *insertInBeginning(struct node *start, int data)
{
        struct node *temp;
        temp = (struct node *)malloc(sizeof(struct node));
        temp->info=data;

        temp->prev=NULL;
        temp->next=start;
        start->prev=temp;
        start=temp;
}//End of insertInBeginng()

void insertAtEnd(struct node *start, int data)
{
        **********************************
        *** COMPLETE THE REQUIRED CODE ***
        **********************************
}//End of insertAtEnd()


void insertAfter(struct node *start, int data, int x)
{
        struct node *temp, *p;
        temp=(struct node*)malloc(sizeof(struct node));
        temp->info=data;

        p=start;
        while(p!=NULL)
        {
                if(p->info==x)
                        break;
                p=p->next;
        }

        if(p==NULL)
                printf("%d not present in the list\n", x);
        else
        {
                temp->prev=p;
                temp->next=p->next;
                if(p->next!=NULL)
                        p->next->prev=temp; //should not be done when p points to last node
                p->next=temp;
        }
}//End of insertAfter()

struct node *insertBefore(struct node *start, int data, int x)
{
        struct node *temp, *p;
        if(start==NULL)
        {
                printf("List is empty\n");
                return start;
        }

        if(start->info==x)
        {
                temp = (struct node *)malloc(sizeof(struct node));
                temp->info=data;

                temp->prev=NULL;
                temp->next=start;
                start->prev=temp;
                start=temp;
                return start;
        }

        p=start;
        while(p!=NULL)
        {
                if(p->info==x)
                        break;
                p=p->next;
        }

        if(p==NULL)
                printf("%d not present in the list\n", x);
        else
        {
                        temp=(struct node *)malloc(sizeof(struct node));
                        temp->info=data;

                        temp->prev=p->prev;
                        temp->next = p;
                        p->prev->next=temp;
                        p->prev=temp;
        }
        return start;
}//End of insertBefore()

struct node *deleteNode(struct node *start, int x)
{
        struct node *temp;

        if(start==NULL)
        {
                printf("List is empty\n");
                return start;
        }

        if(start->next==NULL) //only one node in the list
        {
                if(start->info==x)
                {
                        temp=start;
                        start=NULL;
                        free(temp);
                }
                else
                        printf("Element %d not found\n", x);
                return start;
        }

        //Deletion of first node
        if(start->info==x)
        {
                temp=start;
                start=start->next;
                start->prev=NULL;
                free(temp);
                return start;
        }

        temp=start->next;
        while(temp->next!=NULL)
        {
                if(temp->info==x)
                        break;
                temp=temp->next;
        }

        if(temp->next!=NULL) //node to be deleted is in between
        {
                temp->prev->next=temp->next;
                temp->next->prev=temp->next;
                free(temp);
        }
        else //temp points to last node
        {
                if(temp->info==x) //node to be deleted is last node
                {
                        temp->prev->next=NULL;
                        free(temp);
                }
                else
                                printf("Element %d not fount\n", x);
        }

return start;
}

struct node *reverseList(struct node*start)
{
        struct node *p1, *p2;

        if(start==NULL)
                return;

        p1=start;
        p2=p1->next;
        p1->next=NULL;
        p1->prev=p2;
        while(p2!=NULL)
        {
                p2->prev=p2->next;
                p2->next=p1;
                p1=p2;
                p2=p2->prev;
        }
        start=p1;
        return start;
} //End of reverseList()

Answer 1

The completed code is given below

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

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

struct node *createList(struct node *start);
void displayList(struct node *start);
struct node *insertInEmptyList(struct node *start, int data);
struct node *insertInBeginning(struct node *start, int data);
void insertAtEnd(struct node *start, int data);
void insertAfter(struct node *start, int data, int x);
struct node *insertBefore(struct node *start, int data, int x);
struct node *deleteNode(struct node *start, int data);
struct node *reverseList(struct node *start);

int main()
{
int choice, data, x;
struct node *start=NULL;

start=createList(start);

while(1)
{
printf("\n");
printf("1.Display List\n");
printf("2.Insert in empty list\n");
printf("3.Insert a node in beginning of the list\n");
printf("4.Insert a node at the end of the list\n");
printf("5.Insert a node after a specified node\n");
printf("6.Insert a node before a specified node\n");
printf("7.Delete a node\n");
printf("8.Reverse the list\n");
printf("9.Quit\n");
printf("Enter your choice : ");
scanf("%d", &choice);

if (choice == 9)
break;

switch(choice)
{
case 1:
displayList(start);
break;
case 2:
printf("Enter the element to be inserted : ");
scanf("%d", &data);
start=insertInEmptyList(start,data);
break;
case 3:
printf("Enter the element to be inserted : ");
scanf("%d", &data);
start=insertInBeginning(start, data);
break;
case 4:
printf("Enter the element to be inserted : ");
scanf("%d", &data);
insertAtEnd(start, data);
break;
case 5:
printf("Enter the element to be insert : ");
scanf("%d", &data);
printf("Enter the element after which to insert : ");
scanf("%d", &x);
insertAfter(start, data, x);
break;
case 6:
printf("Enter the element to be inserted : ");
scanf("%d", &data);
printf("Enter the element before which to insrt : ");
scanf("%d", &x);
start=insertBefore(start, data, x);
break;
case 7:
printf("Enter the element to be deleted : ");
scanf("%d", &data);
start=deleteNode(start, data);
break;
case 8:
start=reverseList(start);
break;
default:
printf("Wrong choice\n");

} //end of switch
} //end of while
} //end of main

struct node *createList(struct node *start)
{
int i, n, data;
printf("Enter the number of nodes : ");
scanf("%d", &n);
start=NULL;

if (n==0)
return start;

printf("Enter the first element to be inserted : ");
scanf("%d", &data);
start=insertInEmptyList(start, data);

for (i=2; i<=n; i++)
{
printf("Enter the next element to be inserted : ");
scanf("%d", &data);
insertAtEnd(start, data);
}
return start;
}//End of createList()

void displayList(struct node *start)
{
struct node *p;
if (start==NULL)
{
printf("List is empty\n");
return;
}

p=start;
printf("List is :\n");
while(p!=NULL)
{
printf("%d ", p->info);
p=p->next;
}
printf("\n");
} //End of displayList()

struct node *insertInEmptyList(struct node *start, int data)
{
struct node *temp;
temp = (struct node *)malloc(sizeof(struct node));
temp->info=data;
return temp;
}//End of insertInEmptyList()

struct node *insertInBeginning(struct node *start, int data)
{
struct node *temp;
temp = (struct node *)malloc(sizeof(struct node));
temp->info=data;

temp->prev=NULL;
temp->next=start;
start->prev=temp;
start=temp;
}//End of insertInBeginng()

void insertAtEnd(struct node *start, int data)
{
struct node *temp;
temp = (struct node *)malloc(sizeof(struct node));
temp->info=data;
struct node* temp1=start;
while(temp1!=NULL && temp1->next!=NULL){
temp1=temp1->next;
}
if(temp1){
temp1->next=temp;
}
else if(start==NULL){
start=temp;
}
}//End of insertAtEnd()

void insertAfter(struct node *start, int data, int x)
{
struct node *temp, *p;
temp=(struct node*)malloc(sizeof(struct node));
temp->info=data;

p=start;
while(p!=NULL)
{
if(p->info==x)
break;
p=p->next;
}

if(p==NULL)
printf("%d not present in the list\n", x);
else
{
temp->prev=p;
temp->next=p->next;
if(p->next!=NULL)
p->next->prev=temp; //should not be done when p points to last node
p->next=temp;
}
}//End of insertAfter()

struct node *insertBefore(struct node *start, int data, int x)
{
struct node *temp, *p;
if(start==NULL)
{
printf("List is empty\n");
return start;
}

if(start->info==x)
{
temp = (struct node *)malloc(sizeof(struct node));
temp->info=data;

temp->prev=NULL;
temp->next=start;
start->prev=temp;
start=temp;
return start;
}

p=start;
while(p!=NULL)
{
if(p->info==x)
break;
p=p->next;
}

if(p==NULL)
printf("%d not present in the list\n", x);
else
{
temp=(struct node *)malloc(sizeof(struct node));
temp->info=data;

temp->prev=p->prev;
temp->next = p;
p->prev->next=temp;
p->prev=temp;
}
return start;
}//End of insertBefore()

struct node *deleteNode(struct node *start, int x)
{
struct node *temp;

if(start==NULL)
{
printf("List is empty\n");
return start;
}

if(start->next==NULL) //only one node in the list
{
if(start->info==x)
{
temp=start;
start=NULL;
free(temp);
}
else
printf("Element %d not found\n", x);
return start;
}

//Deletion of first node
if(start->info==x)
{
temp=start;
start=start->next;
start->prev=NULL;
free(temp);
return start;
}

temp=start->next;
while(temp->next!=NULL)
{
if(temp->info==x)
break;
temp=temp->next;
}

if(temp->next!=NULL) //node to be deleted is in between
{
temp->prev->next=temp->next;
temp->next->prev=temp->next;
free(temp);
}
else //temp points to last node
{
if(temp->info==x) //node to be deleted is last node
{
temp->prev->next=NULL;
free(temp);
}
else
printf("Element %d not fount\n", x);
}

return start;
}

struct node *reverseList(struct node*start)
{
struct node *p1, *p2;

if(start==NULL)
return;

p1=start;
p2=p1->next;
p1->next=NULL;
p1->prev=p2;
while(p2!=NULL)
{
p2->prev=p2->next;
p2->next=p1;
p1=p2;
p2=p2->prev;
}
start=p1;
return start;
} //End of reverseList()

The output is