compile
char* list_users(const User *curr) {
    const User *og_user = curr;
    char *user_list = NULL;
    int size = 11;
    while (curr != NULL) {
        size += strlen(curr->name) + 3;
        curr = curr->next;
    }

    user_list = malloc(sizeof(char)*size);

    if (user_list == NULL) {
        perror("malloc");
        exit(1);
    }
    else {
        strcat(user_list, "User List\r\n");
        curr = og_user;
        while (curr != NULL) {
            strcat(user_list, "\t");
            strcat(user_list, curr->name);
            strcat(user_list, "\r\n");
            curr = curr->next;
        }
    }
    return user_list;
}