Linked List in C - c

Question

Although not requirement of my course, I am trying to implement single and double linked list to ensure I understand the concepts. I have worked out most of the issues I think except for one that I have tried to debug and printf my way out of. Although I have read different posts I cannot find out why they are not working similarly.
One my insert function when the while(h != NULL) kicks out I have to check the last item one more time because it would skip it. I thought about a do/while loop but that would not work.
I have the exact same loop for the search function and it finds the last item in the list using while(h != NULL) instead of kicking me before processing it.
Here is the loop that works from the search function,
while(h != NULL) //check list
if(h->val == s)
return true;
else
h = h->next;
Here is the loop that does not from the insert function, this one does not end up using the final value in the linked list before exiting the loop. If you read in the full code before I had to check if if (t->next == NULL && t->val > n) to get it to search the last item.
while(t->next != NULL) //assigns it in the middle
{
if(t->val < n)
t = t->next;
else
{
node* tt = t->prev;
tt->next = a;
a->next = t;
a->prev = t->prev;
t->prev = a;
return h; //returns original
}
}
Thanks in advance and hopefully I am explaining it. Difficult as I am attempting to learn what I do not know.
#include <stdio.h>
#include <stdlib.h> //for rand();
#include <stdbool.h> //bool function
typedef struct _node
{
int val;
struct _node* next;
struct _node* prev;
} node;
node* create(int n, node* h);
node* insert(int n, node* h);
bool search(int s, node* h);
void print(node* h);
void del(node* h);
int main()
{
node* h = NULL;
for(int i = 0; i < 15; i++)
{
int n = rand() % 15;
h = create(n, h);
}
print(h);
int s = 10; //number to search for
if(search(s, h))
printf("Found Item\n");
else
printf("Item not found\n");
del(h);
}
bool search(int s, node* h)
{
if(h == NULL)
printf("No nodes created to search.\n");
while(h != NULL) //check list
if(h->val == s)
return true;
else
h = h->next;
return false;
}
void del(node* h)
{
node* t = h;
while (h->next != NULL)
{
t = h->next;
h->next = NULL;
free(h);
h = t;
}
free(h);
}
node* insert(int n, node* h)
{
node* a = malloc(sizeof(node));
node* t = h;
if(a == NULL)
{
printf("Failed to create new node\n");
return NULL;
}
a->val = n; //sets new node to have value of n
if(h->val >= n) //assigns the integer to the beginning
{
a->next = t;
t->prev = a;
a->prev = NULL;
h = a; //assigns a new head since it appended the item to the beginning
return h;
}
while(t->next != NULL) //assigns it in the middle
{
if(t->val < n)
t = t->next;
else
{
node* tt = t->prev;
tt->next = a;
a->next = t;
a->prev = t->prev;
t->prev = a;
return h; //returns original
}
}
if (t->next == NULL && t->val > n) //check to see if second to last
{
node* tt = t->prev;
tt->next = a;
a->next = t;
a->prev = t->prev;
t->prev = a;
}
else
{
a->next = NULL;
a->prev = t;
t->next = a;
}
return h;
}
node* create(int n, node* h)
{
if(h == NULL) //create first node in the list
{
h = malloc(sizeof(node));
if(h == NULL)
{
printf("Failed to create first node\n");
return NULL;
}
h->val = n;
h->next = NULL;
h->prev = NULL;
}
else //create additional nodes in the list
h = insert(n, h);
return h;
}
void print(node* h)
{
if(h == NULL)
printf("List is empty\n");
else
while(h != NULL)
{
printf("%i\n", h->val);
h = h->next;
}
}

Answer 1

If I understand your question correctly, you are asking about these lines:
while(t->next != NULL) //assigns it in the middle
{
if(t->val < n)
t = t->next;
else
{
node* tt = t->prev;
tt->next = a;
a->next = t;
a->prev = t->prev;
t->prev = a;
return h; //returns original
}
}
if (t->next == NULL && t->val > n) //check to see if second to last
{
node* tt = t->prev;
tt->next = a;
a->next = t;
a->prev = t->prev;
t->prev = a;
}
else
{
a->next = NULL;
a->prev = t;
t->next = a;
}
and the question is: "How can to avoid repeating the code block from inside the while after the while"
Maybe something like this:
while(1)
{
if(t->val < n)
{
if (t->next == NULL) break;
t = t->next;
}
else
{
//assigns it in the middle
node* tt = t->prev;
tt->next = a;
a->next = t;
a->prev = t->prev;
t->prev = a;
return h; //returns original
}
}
// Add new node at the end
a->next = NULL;
a->prev = t;
t->next = a;