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);
}
}
}
