There won't be any minor charge in trading eventhough we are transacting BTC from one address to another.
so, is that an illusion which Exchanges (BITTREX,CEX.IO,...etc) doing only exchange numbers from 1 account to another??
There are charges for trading in exchanges but those are just the trading fees and not actual transaction(miner)fee. The BTC stays still while the numbers are calculated for the particular account. The exchanges charge upto 0.25% per trade and that is how they make money. The BTC is stored in their wallet and whenever you make a deposit or withdrawal the BTC is directly adjusted from their wallet. This is why some exchanges like yobit has the ability to transfer BTC from 1 account to another without any fees within the exchange.