User *find_user(const char *name, const User *head) {
    // traverse the linked list and check each user for a matching name
    // return the pointer if they exist

    const User *node = head;
    while (node != NULL) {
       if (strncmp(node->name, name, MAX_NAME) == 0) {
           return (User *) node;
       }
       node = node->next;
    }

    return NULL;
}
return a pointer to a User object if a User with name exists in a linked list of Users, and NULL if a User with name does not exist in the linked list of Users. 