Simple linked list

#include <stdlib.h>
#include <stdio.h>

struct node1
{
    int data;
    struct node1* next;
};

void add(int data, struct node1**head)
{
    struct node1* p = *head;
    if(p == NULL)
    {
        p = (struct node1*)malloc(sizeof(struct node1));
        p->data = data;
        p->next = NULL;
        *head = p;
        return;
    }
    else
    {
        while (p->next)
            p = p->next;
        struct node1 *t = (struct node1*)malloc(sizeof(struct node1));
        t->data = data;
        t->next = NULL;
        p->next = t;
    }
}

void display(struct node1**head)
{
    struct node1* p = *head;
    while (p)
    {
        printf("%d", p->data);
        p = p->next;
    }
}

int main()
{
    struct node1* head = NULL;
    add(10, &head);
    add(20, &head);
    add(30, &head);
    display(&head);

}