I'm writing a novel how should i describe one's mind?

Question

like the situation one is talking to himself

but he didn't say that out loud

actually he is thinking that (or maybe soliloquize)

like in this situation how should i write (describe him especially the punctuations)

↓ (they are typing online)

“Wow, you are smarter than I thought!” Yao admires.

I was much smarter than you thought, Stonee thinks aloud, but he did type that to Yao.

He continues typing, "......"

Answer 1

In a discussion you would describe that as "to self".  

"Wow you're smarter than I thought!"  Yao types.

"I'm smarter than you think." Stonee says to himself.

Notice the use of the contraction, fluent English speakers will contract whenever possible.

Answer 2

If someone says something, just write what he says.  He wouldn't say it unless he had thought it first. If the person doesn't say it, but just thinks it, you must make that clear.  But don't keep using "he thought." Use other phrases to convey the same idea.  ""It occurred to him that..."   "It seemed to George that...."