A typical linked list, possibly somewhat crudely implemented.

linked_list.c

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

typedef union _data
{ 
    int i;
    double d;
    void *ptr;
} data_t;

typedef enum _data_type {INTEGER, DOUBLE, STRING, POINTER} data_type_t;

typedef struct _list
{
    union _data data;
    enum _data_type type;
    struct _list *next;
} list_t;


list_t *new_list(data_t data, data_type_t type)
{
    list_t *result = malloc(sizeof(list_t));
    if (result == NULL)
    {
        printf("FAIL");
        return NULL;
    }
    result->data = data;
    result->type = type;
    result->next = NULL;
    return result;
}

void append_to_list(list_t *head, list_t *new_node)
{
    list_t *current = head;
    if (head == NULL) // what are you trying to append at?
        return;
    while (current->next != NULL)
        current = current->next;
    current->next = new_node;
    return head;
}

void print_list(list_t *head)
{
    list_t *current = head;
    int i = 0;
    while (current != NULL)
    {
        char format[] = "%5d %x\n";
        const int position = 5;
        switch (current->type)
        {
            case INTEGER:
                format[position] = 'd';
                break;
            case DOUBLE:
                format[position] = 'f';
                break;
            case STRING:
                format[position] = 's';
                break;
            default:
                format[position] = 'p';
        }
        printf(format, i++, current->data);
        current = current->next;
    }
}

void delete_list(list_t *head)
{
    list_t *current = head;
    while (current != NULL)
    {
        list_t *next = current->next;
        free(current);
        current = next;
    }
}

int main (void)
{
    list_t *list;
    data_t nine, five;
    nine.i = 9;
    five.i = 5;
    list = new_list(five, INTEGER);
    append_to_list(list, new_list(nine, INTEGER));
    append_to_list(list, new_list(five, INTEGER));
    append_to_list(list, new_list(nine, INTEGER));
    append_to_list(list, new_list(five, INTEGER));
    append_to_list(list, new_list(nine, INTEGER));
    append_to_list(list, new_list(five, INTEGER));
    append_to_list(list, new_list(nine, INTEGER));
    append_to_list(list, new_list(five, INTEGER));
    append_to_list(list, new_list(nine, INTEGER));
    append_to_list(list, new_list(five, INTEGER));
    append_to_list(list, new_list(nine, INTEGER));
    print_list(list);
    return 0;
}