Let say I have 10 btc now in my own wallet , then on 1 august I got 10 Bitcoin Cash right ? at that tim bcc value $200 , so if i sell my 10 bcc that means i sell my btc too at $200 ? then i lose my both coin just for $2000 , am i wrong ?
Depends on wallet wheather you will get 10 BCC if you change you wallet to BCC one. But let us asume that you get 10 BCC with appropriate wallet then
You are 100%
CORRECT 
If we are talking about exchanges it will happen automatically. That is why i recommended to use different exchange (and/or) account
HOLDING 0 BTC when dealing with BCC
I am really confused because I hear somewhere we are going to get 10BCC if we hold 10BTC. But still, both coins belong to us only, if we hold 10BTC in the exchange so we are going to get 10BCC but actual balance will remain same. (10BTC + 10 BCC) Right.