char username[30];
char password[30];
char password2[30];
int n;

void enterpw() {

        for (n = 0; n <= 30; n++) {
                password[n] = '\0';
                password2[n] = '\0';
        }

        write(1, "\nPassword: ", 11);
        read(0, password, sizeof(password));

        write(1, "Confirm password: ", 18);
        read(0, password2, sizeof(password2));

        for (n = 0; n <= 30; n++) {

                if (password[n] != password2[n]) {
                        write(1, "\nError: Passwords do not match. Try again.\n", 44);
                        enterpw();
                }
        }
}

int main(void) {

        write(1, "\nPlease enter your username: ", 29);
        read(0, username, sizeof(username));

        enterpw();

        int fp = open("user.dat", O_WRONLY | O_CREAT, 0644);
        write(fp, username, sizeof(username));
        write(fp, password, sizeof(password));
        write(fp, password2, sizeof(password2));
        close(fp);

        write(1, "\nPasswords match. Data written to file.\n\n", 41);
        return(0);

}