Most of the program is here already (at the bottom), I am just trying to make it
ID: 3622473 • Letter: M
Question
Most of the program is here already (at the bottom), I am just trying to make it a doubly link list and also use a print backwards function. The program should, for example, display the following at startup:
Enter your choice:
1 to insert an element into the list.
2 to delete an element from the list.
3 to end.
?
Then if the user entered "1" right after the "?" then it would display:
Enter a character:
Then if the user entered "a" it would display:
The list is:
a --> NULL
The list in reverse is:
a --> NULL
?
Then if the user entered 1 to insert an element it would show the following again:
Enter a character: z
Then again, display:
The list is:
a --> z --> NULL
The list in reverse is:
z --> a --> NULL
Below is the code that I have so far. (Sorry the copy and paste formatted it a little funny) Thank you in advance for any and all help.
_______________________________________________________________________
#include
#include
/* self-referential structure */
struct queueNode {
char data; /* define data as a char */
struct queueNode *nextPtr; /* queueNode pointer */
}; /* end structure queueNode */
typedef struct queueNode QueueNode;
typedef QueueNode *QueueNodePtr;
/* function prototypes */
void printQueue( QueueNodePtr currentPtr );
int isEmpty( QueueNodePtr headPtr );
char dequeue( QueueNodePtr *headPtr, QueueNodePtr *tailPtr );
void enqueue( QueueNodePtr *headPtr, QueueNodePtr *tailPtr,
char value );
void instructions( void );
/* function main begins program execution */
int main( void )
{
QueueNodePtr headPtr = NULL; /* initialize headPtr */
QueueNodePtr 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( " %c", &item );
enqueue( &headPtr, &tailPtr, item );
printQueue( headPtr );
break;
/* dequeue value */
case 2:
/* if queue is not empty */
if ( !isEmpty( headPtr ) ) {
item = dequeue( &headPtr, &tailPtr );
printf( "%c has been dequeued. ", item );
} /* end if */
printQueue( headPtr );
break;
default:
printf( "Invalid choice. " );
instructions();
break;
} /* end switch */
printf( "? " );
scanf( "%d", &choice );
} /* end while */
printf( "End of run. " );
return 0; /* indicates successful termination */
} /* end main */
/* display program instructions to user */
void instructions( void )
{
printf ( "Enter your choice: "
" 1 to add an item to the queue "
" 2 to remove an item from the queue "
" 3 to end " );
} /* end function instructions */
/* insert a node a queue tail */
void enqueue( QueueNodePtr *headPtr, QueueNodePtr *tailPtr,
char value )
{
QueueNodePtr newPtr; /* pointer to new node */
newPtr = malloc( sizeof( QueueNode ) );
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. ", value );
} /* end else */
} /* end function enqueue */
/* remove node from queue head */
char dequeue( QueueNodePtr *headPtr, QueueNodePtr *tailPtr )
{
char value; /* node value */
QueueNodePtr 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( QueueNodePtr headPtr )
{
return headPtr == NULL;
} /* end function isEmpty */
/* Print the queue */
void printQueue( QueueNodePtr currentPtr )
{
/* if queue is empty */
if ( currentPtr == NULL ) {
printf( "Queue is empty. " );
} /* end if */
else {
printf( "The queue is: " );
/* while not end of queue */
while ( currentPtr != NULL ) {
printf( "%c --> ", currentPtr->data );
currentPtr = currentPtr->nextPtr;
} /* end while */
printf( "NULL " );
} /* end else */
} /* end function printQueue */
Explanation / Answer
You could use a singly linked list to print the list backwards using recursion like void printReverse(struct node *ptr){ if(ptr->next!=NULL){ printReverse(ptr->nextPtr); } printf("%c",ptr->data); } in doubly linked list just traverse the list and using backward pointer traverse again and print the elements. But for insertion and deletion you have to manipulate the pointers accordingly.
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