just to say hi or just say hi?

都正确，但要看你什么时候用！

I came to his office just to say hi. 我到他办公室只是打个招呼。

To greet someone you run into, you can just say hi.
碰到某人的时候，说声“嗨”打个招呼就好了。

just say hi

or

just want to say hi
just wanna say hi

Just say hi!

Just say yes or no.
你干脆说“行”还是“不行”。

Just say Hi ！正确。

just say hi.

the two are all right