function great(name: string): string {
    return `안녕하세요, ${name}님!`;
}

const add = (a: number, b: number): number => a + b;

function log(message: string, userId?: number): void {
    console.log(`[${userId ?? "Unknown"}] ${message}`);
}

log(add(3, 4).toString());
log(great("타입스크립트"), 135);