Never ever keep your coins in a exchange. If you are not aware with the past news about crypto exchange has been hacked multiple times then try to search it in the web. The most safest way to keep your coins is in a wallet (hardware wallet is the best). It may cost you lots of transaction fees but it is still better than losing all your assets in a exchange. They are the most vulnerable from being hacked right now because hackers can get easy millions once they successfully hacked an exchange so after trading better keep your assets in a wallet.