double linked list with c - c

Question

ok, now i have to make double linked list on c.
there are 7 functions which act on main.
append.
insertAt.
deleteAt.
print.
print_revers.
newnode.
newDLL.
i can amend only 5 functions
append, insertAt, deleteAt, print, print_reverse
finally i can make append,print,print_reverse
however, i can't make insertAt,deleteAt, because of index.
1. i can't understand why the code
else {
while (index-- >= 0) {
temp = temp->next;
}
make memory collide. for using index, i need to move node to collect position and connect to newnode. but it doesn't work...
2. also what's return; 's role? i have not seen such type of return.
3. how can i make deleteAt using index? i think deleteAt and insertAt have quiet similar algoritum. so i try to make insertAt first and deleteAt last. but what i write doesn't work well..
i can find a lot of data of doublelinkedlist on internet. but i can't find using index.... i have been listening c language lecture on only two month, so sorry about the spagettii code...
#include <stdio.h>
#include <stdlib.h>
typedef struct Node {
int val;
struct Node *prev;
struct Node *next;
} Node;
typedef struct {
Node *head;
int size;
} DLL;
Node *newnode(int n)
{
Node *temp = (Node *)malloc(sizeof(Node));
temp->val = n;
temp->prev = NULL;
temp->next = NULL;
return temp;
}
DLL *newDLL() {
DLL *temp = (DLL *)malloc(sizeof(DLL));
temp->head = NULL;
temp->size = 0;
return temp;
}
void append(DLL *list, Node *newnode) {
struct Node* temp = list->head;
struct Node* newNode = newnode;
if (list->head == NULL) {
list->head = newNode;
list->size++;
return;
}
while (temp->next != NULL) {
temp = temp->next;
}
list->size++;
temp->next = newNode;
newNode->prev = temp;
}
void insertAt(DLL *list, int index, Node *newnode) {
struct Node* temp = (Node *)malloc(sizeof(Node));
if (index < 0 || index >= list->size + 1) {
printf("out of range\n");
}
else if (index == 0) {
newnode->next = list->head;
list->head->prev = newnode;
list->head = newnode;
}
else {
while (index-- >= 0) {
temp = temp->next;
}
temp->val = newnode->val;
temp->next = list->head->next;
list->head->next = temp;
temp->prev = list->head;
if (temp->next != NULL)
temp->next->prev = temp;
}
}
void deleteAt(DLL *list, int index) {
//save reference to first link
struct Node* temp = (Node *)malloc(sizeof(Node));
//if only one link
if (list->head->next == NULL) {
list->head->prev = NULL;
}
else {
list->head->next->prev = NULL;
}
list->head = list->head->next;
//return the deleted link
return;
}
void print(DLL *list) {
struct Node* temp = list->head;
printf("Forward: ");
while (temp != NULL) {
printf("[%d] ", temp->val);
temp = temp->next;
}
printf("\n");
}
void print_reverse(DLL *list) {
struct Node* temp = list->head;
if (temp == NULL) return; // empty list, exit
// Going to last Node
while (temp->next != NULL) {
temp = temp->next;
}
// Traversing backward using prev pointer
printf("Reverse: ");
while (temp != NULL) {
printf("[%d] ", temp->val);
temp = temp->prev;
}
printf("\n");
}
int main() {
DLL *list = newDLL();
int i;
for (i = 1; i < 6; i++) {
append(list, newnode(i));
}
print(list);
deleteAt(list, -1);
deleteAt(list, 5);
deleteAt(list, 0);
print(list);
deleteAt(list, 2);
print(list);
deleteAt(list, 2);
print(list);
insertAt(list, -1, newnode(6));
insertAt(list, 3, newnode(6));
insertAt(list, 0, newnode(7));
print(list);
insertAt(list, 1, newnode(8));
print(list);
insertAt(list, 4, newnode(9));
print(list);
print_reverse(list);
return 0;
}

Answer 1

The part where you insert at index has problems:
temp = malloc is wrong, it should start with temp = head.
in the insertion:
temp->val = newnode->val;
temp->next = list->head->next;
list->head->next = temp;
temp->prev = list->head;
temp->next should not be head->next, it should be newnode. newnode->next should be temp->next etc.