Program going into infinte loop instead of calling the function? - c

Question

I was practicing a bit of linked list and I was trying to add elements into sorted doubly linked list. However when I call the the function to add the element in the list, instead of calling the function, program goes into an infinte loop. I have checked the the program does not enter the function adding print statement at start of function. Here's the whole program:
#include<stdio.h>
#include<stdlib.h>
struct node
{
int info;
struct node* next;
struct node* prev;
};
struct node* sortedInsert(struct node* head, int data)
{
printf("x" );
struct node* res=head;
struct node* ptr=(struct node*)malloc(sizeof(struct node));
ptr->info=data;
ptr->next=NULL;
ptr->prev=NULL;
printf("X");
if(head==NULL)
return ptr;
else if(ptr->info<=head->info)
{
ptr->next=head;
head->prev=NULL;
res=ptr;
return res;
}
else
{
while(head!=NULL)
{
if(head->info>=ptr->info)
{
ptr->prev=head->prev;
ptr->next=head;
head->prev=ptr;
return res;
}
}
}
}
struct node* push(struct node* head)
{
struct node* ptr=(struct node*)malloc(sizeof(struct node));
int n;
printf("Enter size: ");
scanf("%d",&n);
printf("Enter elements: ");
for(int i=0;i<n;i++)
{
if(head==NULL)
{
scanf("%d",&ptr->info);
ptr->next=NULL;
ptr->prev=NULL;
head=ptr;
}
else
{
struct node* temp=(struct node*)malloc(sizeof(struct node));
scanf("%d",&temp->info);
temp->next=NULL;
temp->prev=ptr;
ptr->next=temp;
ptr=temp;
}
}
return head;
}
void display(struct node* head)
{
struct node *res;
for(res=head;res!=NULL;res=res->next)
printf("%d\t",res->info);
printf("\n");
}
int main()
{
struct node* head1=NULL;
head1=push(head1);
display(head1);
int num;
printf("Enter number: ");
scanf("%d",&num);
printf("%d\n",num);
head1=sortedInsert(head1,num);
display(head1);
return 0;
}
Output is:
Enter size: 4
Enter elements: 1 2 4 5
1 2 4 5
Enter number: 3
3

Answer 1

It is because you are not incrementing the head to point next node in the while loop.
Also once you found the position in the list where new node to be inserted you need to make prev node point to new node
head->prev->next = ptr; other wise your list will break;
Your code should look like below.
struct node* sortedInsert(struct node* head, int data)
{
.......
.......
while(head!=NULL)
{
if(head->info>=ptr->info)
{
ptr->prev=head->prev;
ptr->next=head;
head->prev->next = ptr; // to make prev node to point new node
head->prev=ptr;
return res;
}
head=head->next; // Increment the head to point next node.
}
.......
}