Stack Linked list

#include<stdio.h>
#include<stdlib.h>
struct std
{
    int id;
    struct std *next;
    struct std *prev;
}*start=NULL,*end=NULL,*top=NULL;

void f_insert()
{
    struct std *newnode,*current;
    newnode=(struct std*)malloc(sizeof(struct std));
    printf("Enter the ID: ");
    scanf("%d",&newnode->id);
    newnode->next=NULL;
    newnode->prev=NULL;
    current=start;
    if(start==NULL){
        start=newnode;
        end=newnode;
    }
    else{
    newnode->next=current;
    current->prev=newnode;
    current=current->prev;
    start=current;
    }
    top=start;
    printf("POP successful\n");
}

void count()
{
    struct std *current;
    int count=0;
    current=start;
    if(start==NULL)
        printf("stack is empty\n");
    else{
    while(current!=NULL)
    {
        count++;
        current=current->next;
    }
    printf("\nThere are %d number of nodes.\n\n",count);
    }
}

void l_delete()
{
    struct std *current,*temp,*temp1,*temp2;
    current=start;
    if(start==NULL)
        printf("stack is empty\n");
    else if(start->next==NULL){
        start=NULL;
        end=NULL;
        top=start;
    }
    else{
        start=current->next;
        (current->next)->prev=NULL;
        top=start;
    }
    printf("\ndeleted successfully\nThe element is %d\n",current->id);
}

void display()
{
    struct std *current;
    current=start;
    if(start==NULL)
        printf("stack is empty\n");
    else{
        count();
        printf("\nThe Top value is : %d\n",top->id);
        printf("\nThe link list by forward display:\n");
    while(current!=NULL)
    {
        printf("%d",current->id);
        if(current->next!=NULL)
             printf("-->");
        current=current->next;
    }
    printf("\n");
    }
}

int main()
{
    while(1){
        int n;
        printf("\n1. push\n2. Pop\n3. display\nchose: ");
        scanf("%d",&n);
        if(n==1)
             f_insert();
        else if(n==2)
             l_delete();
        else if(n==3)
             display();
    }
    return 0;
}