Doubly Linked List Delete Function Error - c

Question

I have written the following program but the problem is in Delete function.Whenever i am trying to delete the value at first position.The whole list is lost don't know why.If i try to display list after that then some garbage values are printed.The function is working perfectly for other positions.
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<assert.h>
struct Student
{
int rno;
char name[20];
struct Student *next;
struct Student *prev;
};
void Display(struct Student *head)
{
assert(head!=NULL);
while(head!=NULL)
{
printf("%d\t%s\t",head->rno,head->name);
head=head->next;
}
}
struct Student *Insert(struct Student *head,const int position,const int rno,const char name[])
{
//printf("%s\n",__FUNCTION__);
struct Student *temp=(struct Student *)malloc(sizeof(struct Student));
struct Student *traverse=head;
int pos=position;
if(temp==NULL)
exit(-1);
temp->rno=rno;
strcpy(temp->name,name);
temp->next=NULL;
temp->prev=NULL;
// printf("%s\n",__FUNCTION__);
if(pos==1)
{
if(head==NULL)
{
head=temp;
}
else
{
temp->next=head;
head->prev=temp;
head=temp;
}
}
else
{
for(traverse=head,pos=position;traverse->next!=NULL&&pos-2!=0;traverse=traverse->next,pos--);
if(traverse==NULL || pos-2!=0)
{
printf("Invalid Position");
}
else
{
temp->next=traverse->next;
if(temp->next!=NULL)
temp->next->prev=temp;
temp->prev=traverse;
traverse->next=temp;
}
}
return head;
}
void DeleteAll(struct Student *head)
{
struct Student *temp=head;
while(temp->next!=NULL)
{
head=head->next;
free(temp);
temp=head;
}
free(temp);
}
void Delete(struct Student *head,int pos)
{
assert(head!=NULL);
struct Student *temp=head;
struct Student *traverse=head;
int position=pos;
if(position==1)
{
if(head->next!=NULL)
head=head->next;
head->prev=NULL;
temp->next=NULL;
free(temp);
}
else
{
while(traverse->next!=NULL&&position-1!=0)
{
traverse=traverse->next;
position--;
}
if(traverse==NULL || position-1!=0)
{
printf(".............Invalid position..........\n");
}
else
{
traverse->prev->next=traverse->next;
if(traverse->next)
traverse->next->prev=traverse->prev;
}
}
}
struct Student *CreateStudentList(const int no_of_students)
{
struct Student *head=NULL;
int i;
int rno;
char name[20];
for(i=0;i<no_of_students;i++)
{
printf("Enter roll number and name:");
scanf("%d%s",&rno,name);
head=Insert(head,i+1,rno,name);
}
return head;
}
void SimulateDoublyLinkedList()
{
struct Student *cdscpp2013=NULL;
int no_of_students;
int choice,rno,position;
char name[20];
while(choice!=5)
{
if(NULL==cdscpp2013)
{
printf("Enter number of students:");
scanf("%d",&no_of_students);
cdscpp2013=CreateStudentList(no_of_students);
}
else
{
printf("\nMenu Operations\nPress 1 for Insert\nPress 2 for Delete\nPress 3 for DeleteAll\nPress 4 for Display\nPress 5 for Exit\nEnter your choice:");
scanf("%d",&choice);
switch(choice)
{
case 1:
printf("Enter roll number and name to ininsert:");
scanf("%d%s",&rno,name);
printf("Enter position to insert:");
scanf("%d",&position);
cdscpp2013=Insert(cdscpp2013,position,rno,name);
break;
case 2:
printf("Enter position to delete:");
scanf("%d",&position);
Delete(cdscpp2013,position);
break;
case 3:
DeleteAll(cdscpp2013);
break;
case 4:
Display(cdscpp2013);
break;
case 5:
exit(1);
default:
printf("Invalid choice....Please Enter proper option.....");
}
}
}
}
int main()
{
SimulateDoublyLinkedList();
}

Answer 1

When you remove the first element of a list, the caller must update its reference to the list. So your Delete function must return the pointer to the first element of the resulting list.
In this kind of operation I also find useful to use pointers to pointers... this would simplify a lot your code.

Answer 2

try this for delete this should work -
as temp = head , the temp->next =null will make the whole list disappear
//just removed temp->next = null;
if(position==1) {
if(head->next!=NULL)
head=head->next;
head->prev=NULL;
free(temp);
}
Edited --
make delete function to return the head pointer and in the switch case use this
cdscpp2013=Delete(cdscpp2013,position);
instead of this
Delete(cdscpp2013,position);
then change the same for deleteall function - it should work :)