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

    User *node = head;
    while (node->next != NULL) {
       if (strncmp(node->name, name, MAX_NAME) == 0) {
           return node;
       }
       node = node->next;
    }
    return NULL;
}
traverse a linked list of User objects and return the pointer to the user with the given name, or NULL if it does not exist