am not sure/I'm not sure

[GeneD]

I think the x means "y" but am not sure if it does.
I think the x means "y", but I'm not sure if it does.

Are these sentences natural? I mean the structure of the sentences.

 

[Rover_KE]

They are both correct.

I prefer #2 (if you had numbered them).

 

[GeneD]

Is #1 used in speech?

 

[Rover_KE]

Some people might say it. I choose not to.

 

[teechar]

I would end those with "... if it does."

 

[GeneD]

I would end those with "... if it does."

I was suspicious of them but didn't know the right way to say it. Thanks for the correction.

 

[Tarheel]

I think the listener would understand that "I" is supposed to be in there (in the first one).