Doubly Linked List

manjotpahwa's Avatar, Join Date: Apr 2010
Light Poster
I wrote the following code, can anyone tell me why is it not working, I was unable to find a reason...

//*************************SERIOUS PROBLEM, NOT WORKING******************
Code:
//DOUBLY LINKED LIST

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

struct dll
{
int info;
struct dll *next;
struct dll *prev;
};
struct dll *head = NULL, *tail = NULL, *temp;

void append();
void insafter();
void delete();
void display();

void main()
{
int choice;
do
{
printf("Enter your choice:\n");
printf("1.Append Node\n2.Insert After a Node\n3.Delete the First Node\n4.Display\n5.Exit");
scanf("%d", &choice);
switch(choice)
	{
	case 1:
		append();
		break;
	case 2:
		insafter();
		break;
	case 3:
		delete();
		break;
	case 4:
		display();
	case 5:
		exit(1);
	default:
	printf("Invalid choice!\n");
	}
}while(choice!=4);
}

void append()
{
int x;
printf("Enter element you wish to push\n");
scanf("%d", &x);
temp->info = x;
if(head==tail && head==NULL)
	{
	temp = head;
	temp->next = temp;
	temp->prev = NULL;
	}
else
	{
	tail->next = temp;
	temp->prev = tail;
	}
tail = temp;
temp->next = NULL;
}

void insafter() //I assume user inputs this option after he has made a list, no condition check for empty list
{
int x, added_item;
printf("Enter the information of the node after which you want to insert your new node\n");
scanf("%d", &x);
temp = head;
while(temp!=NULL)
	{
	while(temp->info!=x)
	temp= temp->next;
	}//now we have the node temp after which we insert our node
printf("Enter item to be added\n");
scanf("%d", &added_item);
struct dll *p;
p->info = added_item;
p->next = temp->next;
p->prev = temp;
temp->next = p;
}

void delete() //allows deleting only from head
{
temp = head;
if(head==NULL)
printf("List empty, nothing to delete\n");
else
printf("Deleted element: %d", temp->info);
head = head->next;
free(temp);
}

void display()
{
temp = head;
if(head==NULL)
printf("Doubly Linked List empty\n");
else
while(temp!=NULL)
	{
	printf("%d", temp->info);
	temp = temp->next;
	}
}

Last edited by shabbir; 14Apr2010 at 21:08.. Reason: Code blocks
0
virxen's Avatar, Join Date: Nov 2009
Pro contributor
erros and solution

Code:
............
scanf("%d", &choice);
getchar();//add this for "garbage" collection
switch(choice){
...........
Code:
    case 4:
        display();
        break;//add this otherwise when it finishes it will go to case 5 and exit.
    case 5:

Code:
void delete1();//change the name delete because it exists in c++ compilers
............
void delete1(){
........
}
Code:
void display(){//i think this look better
    temp = head;
    if(head==NULL){
        printf("Doubly Linked List empty\n");
    }
    else{
        printf("\nNULL ");
        while(temp!=NULL){
           printf("<- %d ->", temp->info);
           temp = temp->next;
       }
       printf("NULL\n");
    }
}
Code:
void append(){//do not forget malloc
    int x;
    printf("Enter element you wish to push\n");
    scanf("%d", &x);
    getchar();
    temp=(struct dll *)malloc(sizeof(struct dll));
    temp->info = x;
    if(head==tail && head==NULL){
       temp->next = NULL;
       temp->prev = NULL;
       head=temp;
       tail = temp;
    }else{
       tail->next = temp;
       temp->prev = tail;
       temp->next = NULL;
       tail = temp;
    } 
}
also since its a double list you want 2 display functions
a)from head to tail (the one you wrote)
b)from tail to head

Code:
void display2(){//b)from tail to head
    temp = tail;
    if(tail==NULL){
        printf("Doubly Linked List empty\n");
    }
    else{
        printf("\nNULL ");
        while(temp!=NULL){
           printf("<- %d ->", temp->info);
           temp = temp->prev;
       }
       printf("NULL\n");
    }
}

with this try to correct the other mistakes you have done.
0
virxen's Avatar, Join Date: Nov 2009
Pro contributor
and for choice-->2

Code:
void insafter(){ //I assume user inputs this option after he has made a list, no condition check for empty list
    int x, added_item;
    printf("Enter the information of the node after which you want to insert your new node\n");
    scanf("%d", &x);
    getchar();
    temp = head;
    while(temp!=NULL){
       if (temp->info==x) break;
        temp= temp->next;
    }//now we have the node temp after which we insert our node
    if (temp==NULL){
        printf("\n the value was not found in the list!\n");
        return;
    }
    printf("Enter item to be added\n");
    scanf("%d", &added_item);
    getchar();
    struct dll *p;
    p=(struct dll *)malloc(sizeof(struct dll));
    p->info = added_item;
    p->next = temp->next;
    p->prev = temp;
    temp->next = p;
}
manjotpahwa like this