I am trying to write a program to make a list of books using linked list. I am using C language. My program crashes as soon as I finish entering the list. It is supposed to print the list before exiting. Any ideas ?

//Defining what libraries should be included.
#include <stdio.h>

//Defining the linked list structure
typedef struct node
   void *data_ptr;
   struct node *link;

// Create node function
NODE *create_node (void *item_ptr)
   NODE *n_ptr;
   // Allocate a node in dynamic memory.
   n_ptr = (NODE *) malloc (sizeof (NODE));
   n_ptr->data_ptr = item_ptr;
   n_ptr->link = NULL;
   return n_ptr;
//Function main begins program execution
int main (void)
   //Definning variables
   int *new_data;
   int *node_ptr;
   NODE *node, *head;
   char bookTitle[20];
   int x;

   //Tells the user how to exit the program.   
   printf("Enter 'end' to stop the program\n"); 
   printf("Enter the title of the book : ");

   while (strcmp(bookTitle,"end") != 0)//Beginning of while loop

   // Allocate memory and create data to pass to the node
   new_data = (void *) malloc (sizeof (char)*20);
   *new_data = bookTitle;

   // Calling the create_node function with data that was just created.
   node = create_node (new_data);

   // Link it to the previous node when created.
   node->link = create_node(new_data);

   // Create a head node to keep track of the beginning of the list
   head = node;

   printf("Enter the title of the book : ");
   // Transverse the list and print
   x = 0;
   if (node == NULL)//Check whether the list is empty
      printf("\nThe list is empty");//Print error
      while (node != NULL)//While loop to print the list
         printf ("\nThe title of the book is: %s", *((char *) node->data_ptr));
         node = node->link;

   system ("PAUSE");
   return 0;// indicate the program ended successfully

}// end of fucntion main

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What's the use of allocating memory in line 42 ? Can you explain it ?

secondly, i have tracked what you are trying to do, but you have made your code damn complex which can be much simpler than this. (anyways, it doesn't matter here)

I allocating memory so that a new node can be created to store the user input.

Line 43 does not copy the string to your newly allocated memory. It sets the first 4 bytes to the address of the start of the bookTitle array. You should use strcpy to do this instead. You then store that data and try to print it later. This could be causing your crash.

Also, you are not linking all your nodes together. Each iteration you call create_node twice, meaning you allocate space for one node, then you link it to a newly allocated node. The second node never gets linked to anything.

Your crash might be related to one of these two bugs or something else.

Line 27:U decleared new_data as integer pointer,
Line 43:U are assigning address of booktitle(string address) to new_data (integer pointer)
so the copy is not happening sucessfully,so u can use memcpy() or strcpy().also u can change the type of new_data.

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