-군요, -구나, and -군 grammar = I see that, I didn't realize that ~express surprise upon learning something new

-군요, -구나, and -군 grammar grammar = I see that, I didn't realize that, ! ~ express surprise about something new

Usage:
- Express surprise or wonder upon learning something new either from direct observation or experience or hearing = 'I see that', 'I didn't realize that', or '!' in English

- The formal style -군요 / -는군요 is mostly used in books
- The informal style -구나 / -군 is often used in casual speaking when speaking to oneself or to friends or to younger persons.

Tense:

1. V + 는군요 / -는구나
먹다 --> 먹는군요 / 먹는구나
사다 --> 사는군요 / 사는구나
운동하다 --> 운동하는군요 / 운동하는구나
*만들다 --> 만드는군요 / 만드는구나 

2. A +군요 / -구나 / -군
크다 --> 크군요 / 크구나
덥다 --> 덥군요 /덥구나
피곤하다 --> 피곤하군요 / 피곤하구나

3. N +(이)군요 / (이)구나  / -군
의사이다 --> 의사(이)군요 / 의사(이)구나
학생이다 --> 학생이군요 / 학생이구나


Examples

1. 눈이 나쁘군요.
Your vision is bad indeed.

2. 아이스크림을 좋아하는군요.
You really like ice cream!

3. 감기가 걸렸군요.
(I see that) You have caught a cold.

4. 우산 있어요? 지금 밖에 비가 와요.
- 정말 비가 오는군요. 우산이 없는데 어떻게 하죠?
Do you have an umbrella? It's raining outside now.
- It's really raining! I don't have an umbrella,  what shall I do?

5. 토니 씨, 인사하세요. 이분이 우리 회사 사장님이세요.
- 아, 사장님이시군요. 안녕하세요.
Tony, please say hello. This is our company president.
- Oh, the company president. Nice to meet you.

6. 엄마, 오늘 학교에서 일이 있어서 늦게 왔어요.
- 응, 그래서 늦었구나.
Mom, I was busy at school today, so I came home late.
- Okay. So that's why you're late.

7. 제 여자 친구 사진이에요.
- 여자 친구가 예쁘구나!
It's my girlfriend picture.
- Your girlfriend is beautiful indeed!

8. 점심시간인데 밥을 안 먹어?
-아, 벌써 점심시간이구나!
It's lunch time,  but don't you have lunch?
- Oh, I see it's already lunch time!

9. 벌써 12월이구나!

(I didn't realized that) it's already Dec!

10. 이 섬은 진짜 넓구나!

(I see that) this island is really big!

11. 니가 매우 똑똑하구나!

(I see that) You are very smart!

12. 지구 표면은 거의 다 물구나!

(I didn't realize that) Almost all of the Earth's surface is water!

13. 생명보험이 그렇게 중요하구나!

(I didn't realize that) Life insurance is so important!

14. 이 돌의 표면이 아주 부드럽구나!

(I see that) The surface of this stone is so smooth!

15. 너도 암호를 모르는구나!

You also don't know the password either!

16. 우리 아들이 영어를 아주 잘하는군요.

(I didn't realize that) our son speaks English very well.