Please do not delete and reinstall the app if it's not necessary. In case of a temporary glitch/error, closing and reopening the app and waiting for the app to fix itself is usually the best option.
If you have to delete the app, please read the following instructions:
Your account is saved either on your device ID or your Game Center. If your Game Center was ON when you installed the app in the first place, your account is safe in your Game Center. In that case, you can safely delete and reload the app, if needed.
If your Game Center was OFF when you installed the app in the first place, your account data is on your device ID. In that case, make sure that your Game Center is OFF before deleting and reinstalling the game. If your account is on your device ID instead of your Game Center, there's a tiny chance that your device ID has changed, and your account can't be found after deleting the account.