doubly LinkedList

// ConsoleApplication3.cpp : Defines the entry point for the console application.
//

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <conio.h>
typedef struct student {
    struct student* next;
    struct student* prev;
    int fnum;
    char firstname[20];
    char lastname[20];
    double grade;
}student;
student input(void);
struct student* Add(student *root);
void output(student *root);

int main()
{
    student* head=NULL;
    int n;
    printf("How many elements do you want to create?");
    scanf_s("%d", &n);
    for (int i = 0; i < n; i++) {
        head=Add(head);
    }
    output(head);
    return 0;
}

student input(void) {
    student a = { 0 };
    printf("Firstname:");
    fgets(a.firstname, sizeof a.firstname, stdin);
    printf("Lastname:");
    fgets(a.lastname, sizeof a.lastname, stdin);
    printf("Firstname:");
    fgets(a.firstname, sizeof a.firstname, stdin);
    printf("fnum");
    scanf_s("%d", &(a.fnum));
    printf("grade");
    scanf_s("%lf", &(a.grade));
    a.next = NULL;
    a.prev = NULL;
    return a;
}

student* Add(student* root) {
    student* p = malloc(sizeof(student));
    student b = input();
    p = &b;
    student* l;
    if (root == NULL) {
        root = p;
        return root;
    }
    for (;;) {
        if (root->next == NULL) {
            if (root->fnum < p->fnum) {
                root->next = p;
                p->prev = root;
                return root;
            }
            else {
                l = root;
                root = p;
                root->next = l;
                l->prev = p;
                return root;
            }
        }
        if (root->fnum < p->fnum) {
            root = root->next;
            continue;
        }
        else {
            l = root;
            root = p;
            root->next = l;
            l->prev = p;
            return root;
        }
    }
    return root;
}

void output(student* root) {
    if (root != NULL) {
        printf("fname %s", root->firstname);
        printf("lname %s",root->lastname);
        printf("fnum %d", root->fnum);
        printf("grade %13.6lf", root->grade);
        output(root->next);
    }
}