Create a doubly linked list and a print backwards function.

I have to create a doubly linked list and a print backwards function. I have the following code. Can someone please help me out here!? Under case 1 if u comment out reverse ( headPtr ) the program will run fine and you can see everything working. But I still need it to print backwards. Thank you in advance.

Code:

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

/* self-referential structure */
	struct listNode {   
	   char data;
	   struct listNode *nextPtr; 
	   struct listNode *prevPtr; 
	};

typedef struct listNode listNode;
typedef listNode *listNodePtr;

/* function prototypes */
	void printQueue( listNodePtr currentPtr );
	int isEmpty( listNodePtr headPtr );
	char dequeue( listNodePtr *headPtr, listNodePtr *tailPtr );
	void enqueue( listNodePtr *headPtr, listNodePtr *tailPtr, 
	   char value );
	void instructions( void );

/* function main begins program execution */
int main( void )
{ 
   listNodePtr headPtr = NULL; /* initialize headPtr */
   listNodePtr tailPtr = NULL; /* initialize tailPtr */
   int choice; /* user's menu choice */
   char item; /* char input by user */

   instructions(); /* display the menu */
   printf( "? " );
   scanf( "%d", &choice );

   /* while user does not enter 3 */
   while ( choice != 3 ) { 

      switch( choice ) { 
         /* enqueue value */
         case 1:
            printf( "Enter a character: " );
            scanf( "\n%c", &item );
            enqueue( &headPtr, &tailPtr, item );
            printQueue( headPtr );
            reverse( headPtr );
            break;
         /* dequeue value */
         case 2:
            /* if queue is not empty */
            if ( !isEmpty( headPtr ) ) { 
               item = dequeue( &headPtr, &tailPtr );
               printf( "%c has been dequeued.\n", item );
            } /* end if */

            printQueue( headPtr );
            break;
         default:
            printf( "Invalid choice.\n\n" );
            instructions();
            break;
      } /* end switch */

      printf( "? " );
      scanf( "%d", &choice );
   } /* end while */

   printf( "End of run.\n" );
   return 0; /* indicates successful termination */
} /* end main */

/* display program instructions to user */
void instructions( void )
{ 
   printf ( "Enter your choice:\n"
           "   1 to add an item to the queue\n"
           "   2 to remove an item from the queue\n"
           "   3 to end\n" );
} /* end function instructions */

/* insert a node a queue tail */
void enqueue( listNodePtr *headPtr, listNodePtr *tailPtr, 
   char value )
{ 
   listNodePtr newPtr; /* pointer to new node */

   newPtr = malloc( sizeof( listNode ) );

   if ( newPtr != NULL ) { /* is space available */ 
      newPtr->data = value;
      newPtr->nextPtr = NULL;

      /* if empty, insert node at head */
      if ( isEmpty( *headPtr ) ) {
         *headPtr = newPtr;
      } /* end if */
      else {
         ( *tailPtr )->nextPtr = newPtr;
      } /* end else */

      *tailPtr = newPtr;
   } /* end if */
   else {
      printf( "%c not inserted. No memory available.\n", value );
   } /* end else */
} /* end function enqueue */

/* remove node from queue head */
char dequeue( listNodePtr *headPtr, listNodePtr *tailPtr )
{ 
   char value; /* node value */
   listNodePtr tempPtr; /* temporary node pointer */

   value = ( *headPtr )->data;
   tempPtr = *headPtr;
   *headPtr = ( *headPtr )->nextPtr;

   /* if queue is empty */
   if ( *headPtr == NULL ) {
      *tailPtr = NULL;
   } /* end if */

   free( tempPtr );
   return value;
} /* end function dequeue */

/* Return 1 if the list is empty, 0 otherwise */
int isEmpty( listNodePtr headPtr )
{ 
   return headPtr == NULL;
} /* end function isEmpty */

/* Print the queue */
void printQueue( listNodePtr currentPtr )
{ 
   /* if queue is empty */
   if ( currentPtr == NULL ) {
      printf( "Queue is empty.\n\n" );
   } /* end if */
   else { 
      printf( "The queue is:\n" );

      /* while not end of queue */
      while ( currentPtr != NULL ) { 
         printf( "%c --> ", currentPtr->data );
         currentPtr = currentPtr->nextPtr;
      } /* end while */

      printf( "NULL\n\n" );
   } /* end else */
} /* end function printQueue */

void reverse( listNodePtr currentPtr)  
{  
   struct listNode *temp = NULL;   

	 /* if queue is empty */
   if ( currentPtr == NULL ) {
      printf( "Queue is empty.\n\n" );
   } /* end if */
   else { 
      printf( "The queue backwards is:\n" );
     /* swap next and prevPtr for all listNodes of  
       doubly linked list */ 
     while (currentPtr !=  NULL)  
     {  
	    temp = currentPtr->prevPtr;  
		currentPtr->prevPtr = currentPtr->nextPtr;  
		currentPtr->nextPtr = temp;  
		currentPtr = currentPtr->prevPtr;
        printf( "%c --> ", currentPtr->data);  
     }        
   }
}

To print reverse, you start at tailPtr and do current = current->prevPtr

You don't need to reorder the entire list.

Can you show me what the code would look like please? Also do you know why I get an erro when I put reverse( headptr ) under case 1?

Yes, it looks like printQueue() with a search and replace.

Thank you very much for your help so far, so do you mean all I do is copy the printQueue code, replace nextPtr with prevPtr and that's it?

Have you tried it yet?