I am writing a program in C and have the code written but am running into a few
ID: 675470 • Letter: I
Question
I am writing a program in C and have the code written but am running into a few errors. Firstly, here is the assignment:
Modify the linked list example in the book so that it is a doubly linked list. Prove that your program works properly by implementing a print backwards function:
/* Fig. 12.3: fig12_03.c
Operating and maintaining a list */
#include <stdio.h>
#include <stdlib.h>
/* self-referential structure */
struct listNode {
char data; /* each listNode contains a character */
struct listNode *nextPtr; /* pointer to next node*/
}; /* end structure listNode */
typedef struct listNode ListNode; /* synonym for struct listNode */
typedef ListNode *ListNodePtr; /* synonym for ListNode* */
/* prototypes */
void insert( ListNodePtr *sPtr, char value );
char delete( ListNodePtr *sPtr, char value );
int isEmpty( ListNodePtr sPtr );
void printList( ListNodePtr currentPtr );
void instructions( void );
int main( void )
{
ListNodePtr startPtr = NULL; /* initially there are no nodes */
int choice; /* user's choice */
char item; /* char entered by user */
instructions(); /* display the menu */
printf( "? " );
scanf( "%d", &choice );
/* loop while user does not choose 3 */
while ( choice != 3 ) {
switch ( choice ) {
case 1:
printf( "Enter a character: " );
scanf( " %c", &item );
insert( &startPtr, item ); /* insert item in list */
printList( startPtr );
break;
case 2:
/* if list is not empty */
if ( !isEmpty( startPtr ) ) {
printf( "Enter character to be deleted: " );
scanf( " %c", &item );
/* if character is found, remove it */
if ( delete( &startPtr, item ) ) { /* remove item */
printf( "%c deleted. ", item );
printList( startPtr );
} /* end if */
else {
printf( "%c not found. ", item );
} /* end else */
} /* end if */
else {
printf( "List is empty. " );
} /* end else */
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 insert an element into the list. "
" 2 to delete an element from the list. "
" 3 to end. " );
} /* end function instructions */
/* Insert a new value into the list in sorted order */
void insert( ListNodePtr *sPtr, char value )
{
ListNodePtr newPtr; /* pointer to new node */
ListNodePtr previousPtr; /* pointer to previous node in list */
ListNodePtr currentPtr; /* pointer to current node in list */
newPtr = malloc( sizeof( ListNode ) ); /* create node */
if ( newPtr != NULL ) { /* is space available */
newPtr->data = value; /* place value in node */
newPtr->nextPtr = NULL; /* node does not link to another node */
previousPtr = NULL;
currentPtr = *sPtr;
/* loop to find the correct location in the list */
while ( currentPtr != NULL && value > currentPtr->data ) {
previousPtr = currentPtr; /* walk to ... */
currentPtr = currentPtr->nextPtr; /* ... next node */
} /* end while */
/* insert new node at beginning of list */
if ( previousPtr == NULL ) {
newPtr->nextPtr = *sPtr;
*sPtr = newPtr;
} /* end if */
else { /* insert new node between previousPtr and currentPtr */
previousPtr->nextPtr = newPtr;
newPtr->nextPtr = currentPtr;
} /* end else */
} /* end if */
else {
printf( "%c not inserted. No memory available. ", value );
} /* end else */
} /* end function insert */
/* Delete a list element */
char delete( ListNodePtr *sPtr, char value )
{
ListNodePtr previousPtr; /* pointer to previous node in list */
ListNodePtr currentPtr; /* pointer to current node in list */
ListNodePtr tempPtr; /* temporary node pointer */
/* delete first node */
if ( value == ( *sPtr )->data ) {
tempPtr = *sPtr; /* hold onto node being removed */
*sPtr = ( *sPtr )->nextPtr; /* de-thread the node */
free( tempPtr ); /* free the de-threaded node */
return value;
} /* end if */
else {
previousPtr = *sPtr;
currentPtr = ( *sPtr )->nextPtr;
/* loop to find the correct location in the list */
while ( currentPtr != NULL && currentPtr->data != value ) {
previousPtr = currentPtr; /* walk to ... */
currentPtr = currentPtr->nextPtr; /* ... next node */
} /* end while */
/* delete node at currentPtr */
if ( currentPtr != NULL ) {
tempPtr = currentPtr;
previousPtr->nextPtr = currentPtr->nextPtr;
free( tempPtr );
return value;
} /* end if */
} /* end else */
return '';
} /* end function delete */
/* Return 1 if the list is empty, 0 otherwise */
int isEmpty( ListNodePtr sPtr )
{
return sPtr == NULL;
} /* end function isEmpty */
/* Print the list */
void printList( ListNodePtr currentPtr )
{
/* if list is empty */
if ( currentPtr == NULL ) {
printf( "List is empty. " );
} /* end if */
else {
printf( "The list is: " );
/* while not the end of the list */
while ( currentPtr != NULL ) {
printf( "%c --> ", currentPtr->data );
currentPtr = currentPtr->nextPtr;
} /* end while */
printf( "NULL " );
} /* end else */
} /* end function printList */
Here is my code and I'll point out there errors with bold:
struct listNode {
char data; /* each listNode contains a character */
struct listNode *nextPtr; /* pointer to next node*/
struct listNode *prevPtr; /* pointer to previous node*/
}; /* end structure listNode */
typedef struct listNode ListNode; /* synonym for struct listNode */
typedef ListNode *ListNodePtr; /* synonym for ListNode* */
/* prototypes */
void insert(ListNodePtr *sPtr, char value);
char delete(ListNodePtr *sPtr, char value); <--- "EXPECTED AN IDENTIFER ON "delete"
int isEmpty(ListNodePtr sPtr);
void printList(ListNodePtr currentPtr);
void printListBackwards(ListNodePtr currentPtr);
void instructions(void);
int main(void)
{
ListNodePtr startPtr = NULL; /* initially there are no nodes */
int choice; /* user's choice */
char item; /* char entered by user */
instructions(); /* display the menu */
printf("? ");
scanf("%d", &choice);
/* loop while user does not choose 3 */
while (choice != 3) {
switch (choice) {
case 1:
printf("Enter a character: ");
scanf(" %c", &item);
insert(&startPtr, item); /* insert item in list */
printList(startPtr);
break;
case 2:
/* if list is not empty */
if (!isEmpty(startPtr)) {
printf("Enter character to be deleted: ");
scanf(" %c", &item);
/* if character is found, remove it */
if (delete(&startPtr, item)) { /* remove item */ <--- "Expression must be a pointer to a complete object type."
printf("%c deleted. ", item);
printList(startPtr);
} /* end if */
else {
printf("%c not found. ", item);
} /* end else */
} /* end if */
else {
printf("List is empty. ");
} /* end else */
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 insert an element into the list. "
" 2 to delete an element from the list. "
" 3 to end. ");
} /* end function instructions */
/* Insert a new value into the list in sorted order */
void insert(ListNodePtr *sPtr, char value)
{
ListNodePtr newPtr; /* pointer to new node */
ListNodePtr previousPtr; /* pointer to previous node in list */
ListNodePtr currentPtr; /* pointer to current node in list */
newPtr = malloc(sizeof(ListNode)); /* create node */ <--- "A value type of void cannot be assigned to an entity type of "ListNodePtr"
if (newPtr != NULL) { /* is space available */
newPtr->data = value; /* place value in node */
newPtr->nextPtr = NULL; /* node does not link to another node */
newPtr->prevPtr = NULL; /* node does not link to previous node */
previousPtr = NULL;
currentPtr = *sPtr;
/* loop to find the correct location in the list */
while (currentPtr != NULL && value > currentPtr->data) {
previousPtr = currentPtr; /* walk to ... */
currentPtr = currentPtr->nextPtr; /* ... next node */
} /* end while */
/* insert new node at beginning of list */
if (previousPtr == NULL) {
newPtr->nextPtr = *sPtr;
*sPtr = newPtr;
} /* end if */
else { /* insert new node between previousPtr and currentPtr */
previousPtr->nextPtr = newPtr;
newPtr->nextPtr = currentPtr;
newPtr->prevPtr = previousPtr;
if (currentPtr != NULL)
currentPtr->prevPtr = newPtr;
} /* end else */
} /* end if */
else {
printf("%c not inserted. No memory available. ", value);
} /* end else */
} /* end function insert */
/* Delete a list element */
char delete(ListNodePtr *sPtr, char value) <---- "Expected an identifer"
{
ListNodePtr previousPtr; /* pointer to previous node in list */
ListNodePtr currentPtr; /* pointer to current node in list */
ListNodePtr tempPtr; /* temporary node pointer */
/* delete first node */
if (value == (*sPtr)->data) {
tempPtr = *sPtr; /* hold onto node being removed */
*sPtr = (*sPtr)->nextPtr; /* de-thread the node */
if ((*sPtr) != NULL)
(*sPtr)->prevPtr = NULL; /* nullify previous node */
free(tempPtr); /* free the de-threaded node */
return value;
} /* end if */
else {
previousPtr = *sPtr;
currentPtr = (*sPtr)->nextPtr;
/* loop to find the correct location in the list */
while (currentPtr != NULL && currentPtr->data != value) {
previousPtr = currentPtr; /* walk to ... */
currentPtr = currentPtr->nextPtr; /* ... next node */
} /* end while */
/* delete node at currentPtr */
if (currentPtr != NULL) {
tempPtr = currentPtr;
previousPtr->nextPtr = currentPtr->nextPtr;
if (currentPtr->nextPtr != NULL)
currentPtr->nextPtr->prevPtr = previousPtr;
free(tempPtr);
return value;
} /* end if */
} /* end else */
return '';
} /* end function delete */
/* Return 1 if the list is empty, 0 otherwise */
int isEmpty(ListNodePtr sPtr)
{
return sPtr == NULL;
} /* end function isEmpty */
/* Print the list then call printListBackwards*/
void printList(ListNodePtr currentPtr)
{
ListNodePtr previousPtr; /* pointer to previous node in list */
/* if list is empty */
if (currentPtr == NULL) {
printf("List is empty. ");
} /* end if */
else {
printf("The list is: ");
/* while not the end of the list */
while (currentPtr != NULL) {
printf("%c --> ", currentPtr->data);
previousPtr = currentPtr;
currentPtr = currentPtr->nextPtr;
} /* end while */
printf("NULL ");
printListBackwards(previousPtr);
} /* end else */
} /* end function printList */
/* Print the list Backwards*/
void printListBackwards(ListNodePtr currentPtr)
{
printf("The list in reverse is: ");
/* while not the end of the list */
while (currentPtr != NULL) {
printf("%c --> ", currentPtr->data);
currentPtr = currentPtr->prevPtr;
} /* end while */
printf("NULL ");
} /* end function printListBackwards */
How can I get this code to work?!
Explanation / Answer
It seems it should work properly.. I havn't find errors in your program.. please clear the cache and try to run again. and before that please check your declarations of the variables.