typedef struct user {
    char name[MAX_NAME];
    char profile_pic[MAX_NAME];  // This is a *filename*, not the file contents.
    struct user *friends[MAX_FRIENDS];
    struct user *next;
} User;



int update_pic(User *user, const char *filename) {
    if (strlen(filename) > MAX_NAME) {
        return 2;
    }
    else if (fopen())

    // checks passed, change filename
    strcpy(user->profile_pic, filename);
    return 0;
}
check for if the file does not exist or cannot be opened