Doubly linklist Implementation in c

linklist.c

#include <stdio.h>
#include<conio.h>
#include <stdlib.h>
#include<malloc.h>
#define null 0
struct node
{
    struct node *prev;
    int data;
    struct node *next;
}*start=null,*temp=null,*last=null;

void create();
void display();
void del();
void insert();

 void main()
{
  int a;

  do
  {
    printf("\n1:Create list");
    printf("\n2:Display");
    printf("\n3:Delete");
     printf("\n4:Insert\n");
     printf("\n\tEnter your option");
     scanf("%d",&a);
     switch(a)
     {
     case 1:
        create();
        break;
     case 2:
        display();
        break;
     case 3:
        del();
        break;
     case 4:
        insert();
     }
     }while(a!=5);


}
void create()
{
    int x;
temp=(struct node*)malloc(sizeof(struct node));
printf("\nEnter Data");
scanf("%d",&x);
temp->data=x;
temp->next=null;
temp->prev=null;
if(start==null)
{
   start=temp ;
   last=temp;

}
else{
    last->next=temp;
    temp->prev=last;
    last=temp;
}
printf("\nList Created");
}

void display()
{

int x;
printf("\n\tEnter option");
printf("\n1:Print from beginning");
printf("\n2:print Reverse");
scanf("\n%d",&x);
switch(x)
{

case 1:
    temp=start;
    while(temp!=null)
    {
        printf("\n%d",temp->data);
        temp=temp->next;
    }
getch();
break;
case 2:
    temp=last;
    while(temp!=null)
    {
        printf("\n%d",temp->data);
        temp= temp->prev;
    }
break;

}}

void del()
{
    int x,y,z;
struct node *ptr;
    printf("\n1:Del from Beginning");
    printf("\n2:Del from middle");
    printf("\n3:Del from last");
    printf("\nEnter your option");
    scanf("%d",&x);
    switch(x)
    {
        case 1:
    temp=start;
    temp=temp->next;
    start=temp;
    break;
        case 3:
            temp=last;
            temp=temp->prev;
            temp->next=null;
            break;
        case 2:
            printf("\nEnter value to be deleted");
            scanf("%d",&y);
            printf("1:One value \n 2: All value");
            scanf("%d",&z);
            if(z==1)
            {
            temp=start;
            while(temp->data!=y)
            {
                temp=temp->next;
            }
            ptr=temp->prev;
            temp=temp->next;
            temp->prev=ptr;
            ptr->next=temp;
            }
            else{
                temp=start;
                while(temp->next!=null)
                {

                    if(temp->data==y)
                    {
                        ptr=temp->prev;
                        temp=temp->next;
                        temp->prev=ptr;
                         ptr->next=temp;

                    } temp=temp->next;
                }
            }
    }
}
void insert()
{
    int x,y;
    printf("\nEnter data to Insert");
    scanf("%d",&y);
    printf("\n1:Enter at Beginning");
     printf("\n2:Enter at Middle");
      printf("\n3:Enter at Last");
      printf("\nEnter your option");
      scanf("%d",&x);
      if(x==1)
      {
          temp=(struct node*)malloc(sizeof(struct node));
          temp->data=y;
          temp->prev=null;
          temp->next=start;
          start->prev=temp;
          start=temp;
      }
      else if(x==2)
      {
          int z;
          struct node *ptr,*p;
          printf("\n\tEnter data After which to Insert");
          scanf("%d",&z);
        temp=start;
        while(temp->data!=z)
        {
            temp=temp->next;
        }
        ptr=temp->next;
        p=(struct node*)malloc(sizeof(struct node));
        p->data=y;
        temp->next=p;
        p->next=ptr;
        ptr->prev=p;
        p->prev=temp;

      }
      else
      {
           temp=(struct node*)malloc(sizeof(struct node));
           temp->data=y;
           last->next=temp;
           temp->prev=last;
           temp->next=null;
           last=temp;



      }

}