関連ワード:  why do you have to return 0 in c++    why do you need to return 0 in c    why do you need return 0 in c++    why do you return 0 in c++    do you have to put return 0 in c++    why do we return 0 in c    why do we use return 0 in c    why do we write return 0 in cpp    what happens if we don't use return 0 in c    is return 0 necessary in c