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#include<stdio.h>
#include<stdlib.h>
struct node
{
    int id;
    struct node *next;
    struct node *prev;
}*start=NULL,*end=NULL;
void create()
{
    int n,i;
    struct node *new_node,*current;
    printf("Enter the number of student: \n");
    scanf("%d",&n);
    for(i=0; i<n; i++)
    {
        new_node=(struct node*)malloc(sizeof(struct node));

        printf("Enter the id of student no %d: \n",i+1);
        scanf("%d",&new_node->id);
        new_node->next=NULL;
        new_node->prev=NULL;
        if(start==NULL&&end==NULL)
        {
            start=new_node;
            end=new_node;
            current=new_node;
        }
        else
        {
            current->next=new_node;
            new_node->prev=current;
            current=new_node;
            end=new_node;
        }
    }
}

void f_insert()
{
    struct node *new_node,*current;
    new_node=(struct node*)malloc(sizeof(struct node));
    printf("\nEnter the first id of student no : \n");
    scanf("%d",&new_node->id);
    new_node->next=NULL;
    new_node->prev=NULL;
    current=start;
    start=new_node;
    new_node->next=current;
    current->prev=new_node;
}

void l_insert()
{
    struct node *new_node,*current;
    new_node=(struct node*)malloc(sizeof(struct node));
    printf("\nEnter the last id of student no : \n");
    scanf("%d",&new_node->id);
    new_node->next=NULL;
    new_node->prev=NULL;
    current=end;
    current->next=new_node;
    new_node->prev=current;
    end=new_node;
}
int search(int s_key)
{
    int pos=0;
    struct node *current;
    current=start;
    while(current!=NULL)
    {
        pos++;
        if(current->id==s_key)
        {
            return pos;
        }
        current=current->next;
    }
    return -1;
}
void mb_insert()
{
    int key,i,pos;
    struct node *temp,*current,*new_node;
    new_node=(struct node*)malloc(sizeof(struct node));
    printf("\nEnter the middle(before) id of student no : \n");
    scanf("%d",&new_node->id);
    new_node->next=NULL;
    new_node->prev=NULL;
    printf("\nEnter the id before the new node insert:\n");
    scanf("%d",&key);
    pos=search(key);
    current=start;
    for(i=1;i<=pos-1;i++)
    {
        current=current->next;
    }
    temp=current->prev;
    temp->next=new_node;
    new_node->prev=temp;
    new_node->next=current;
    current->prev=new_node;

}
void ma_insert()
{
    int key,i,pos;
    struct node *temp,*current,*new_node;
    new_node=(struct node*)malloc(sizeof(struct node));
    printf("\nEnter the middle(after) id of student no : \n");
    scanf("%d",&new_node->id);
    new_node->next=NULL;
    new_node->prev=NULL;
    printf("\nEnter the id after the new node insert:\n");
    scanf("%d",&key);
    pos=search(key);
    current=start;
    for(i=1;i<=pos-1;i++)
    {
        current=current->next;
    }
    //printf("\nCurrent=%d",current->id);
    temp=current->next;
    current->next=new_node;
    new_node->prev=current;
    new_node->next=temp;
    temp->prev=new_node;

}
void delete_ll()
{
    int dkey,pos,i;
    struct node *current,*temp1,*temp2;
    printf("\nEnter the value for deleting:\n");
    scanf("%d",&dkey);
    pos=search(dkey);
    current=start;
    for(i=1;i<=pos-1;i++)
    {
        current=current->next;
    }
    if(current==start)
    {
        temp1=current->next;
        temp1->prev=NULL;
        start=temp1;
    }
    else if(current==end)
    {
        temp1=current->prev;
        temp1->next=NULL;
        end=temp1;
    }
    else
    {
        temp1=current->prev;
        temp2=current->next;
        temp1->next=temp2;
        temp2->prev=temp1;
    }
    printf("\nDelete Successfully.");
}
void f_display()
{
    struct node *current;
    current=start;
    printf("\nThe Link List from start is:\n");
    while(current!=NULL)
    {
        printf("%d-->",current->id);
        current=current->next;
    }
    printf("NULL\n");
}
void b_display()
{
    struct node *current;
    current=end;
    printf("\nThe Link List from last is:\n");
    while(current!=NULL)
    {
        printf("%d-->",current->id);
        current=current->prev;
    }
    printf("NULL\n");
}
void max()
{
    int max=-100000;
    struct node *current;
    current=start;
    while(current!=NULL)
    {
        if(current->id>max)
        {
            max=current->id;
        }
        current=current->next;
    }
    printf("\nThe maximum value is:%d.",max);
}
void sum_avg()
{
    int sum=0,c=0;
    float avg;
    struct node *current;
    current=start;
    while(current!=NULL)
    {
        sum=sum+current->id;
        current=current->next;
    }
    printf("\nThe summation value is:%d.",sum);
}
void count()
{
    int c=0;

    struct node *current;
    current=start;
    while(current!=NULL)
    {
        c++;
        current=current->next;
    }
    printf("\nThe num of node in the LL is:%d.",c);
}
void even_freq()
{
    int even=0;
    struct node *current;
    current=start;
    while(current!=NULL)
    {
        if(current->id%2==0)
        {
            even++;
        }
        current=current->next;
    }
    printf("\nThe total even num is:%d.",even);
}

int main()
{
    int s_key,pos;
    create();
    f_display();
    b_display();
    /*f_insert();
    f_display();
    b_display();
    l_insert();
    f_display();
    b_display();
    printf("\nEnter the id for searching:");
    scanf("%d",&s_key);
    pos=search(s_key);
    if(pos==-1)
    {
        printf("\nNOT FOUND");
    }
    else
    {
        printf("\n FOUND at %d",pos);
    }
    mb_insert();
    f_display();
    b_display();
    ma_insert();
    f_display();
    b_display();*/
    delete_ll();
    f_display();
    b_display();
    max();
    sum_avg();
    count();
    even_freq();
    return 0;


}